Editing Water clock (section)

===Greco-Roman world===
[[File:Clepsydra-Diagram-Fancy.jpeg|thumb|left|An early 19th-century illustration<ref>This engraving is taken from "Rees's Clocks, Watches, and Chronometers 1819–20. The design of the illustration was modified from Claude Perrault's illustrations in his 1684 translation of Vitruvius's Les Dix Livres d'Architecture (1st century BC), of which he describes Ctesibius's clepsydra in great length.</ref> of [[Ctesibius]]'s (285–222 BC) clepsydra from the 3rd century BC. The hour indicator ascends as water flows in. Also, a series of gears rotate a cylinder to correspond to the temporal hours.]]
[[File:Ctesibius' hydraulic clock.jpg|thumb|A modern reconstruction of [[Ctesibius]]' hydraulic clock (clepsydra), at the [[Museum of Ancient Greek Technology|Kotsanas Museum of Ancient Greek Archaeology]] in [[Athens]].]]
The word "[[wiktionary:κλεψύδρα#Ancient Greek|clepsydra]]" comes from the Greek meaning "water thief".<ref>{{cite book |last=Levy |first=Janey |year=2004 |title=Keeping Time Through the Ages: The History of Tools Used to Measure Time |publisher=Rosen Classroom |isbn=9780823989171 |page=[https://archive.org/details/keepingtimethrou0000levy/page/11 11] |quote=The Greeks named the water clock 'clepsydra' (KLEP-suh-druh), which means 'water thief'. |url=https://archive.org/details/keepingtimethrou0000levy/page/11 }}</ref> The Greeks considerably advanced the water clock by tackling the problem of the diminishing flow. They introduced several types of the inflow clepsydra, one of which included the earliest feedback control system.<ref>{{Harvp|Goodenow|Orr|Ross|2007|p=7}}</ref> [[Ctesibius]] invented an indicator system typical for later clocks such as the dial and pointer.<ref name="John G. Landels 35">John G. Landels: "Water-Clocks and Time Measurement in Classical Antiquity", "Endeavour", Vol. 3, No. 1 (1979), pp. 32–37 (35)</ref> The [[Ancient Rome|Roman]] engineer [[Vitruvius]] described early alarm clocks, working with gongs or trumpets.<ref name="John G. Landels 35"/> A commonly used water clock was the simple outflow clepsydra. This small earthenware vessel had a hole in its side near the base. In both Greek and Roman times, this type of clepsydra was used in courts for allocating periods of time to speakers. In important cases, such as when a person's life was at stake, it was filled completely, but for more minor cases, only partially. If proceedings were interrupted for any reason, such as to examine documents, the hole in the clepsydra was stopped with wax until the speaker was able to resume his pleading.<ref>{{Harvnb|Hill|1981|p=6}}</ref>

====Clepsydrae for keeping time====
Some scholars suspect that the clepsydra may have been used as a stop-watch for imposing a time limit on clients' visits in [[Athens|Athenian]] brothels.<ref name="John G. Landels 32">{{cite journal|last=Landels|first=John G.|title=Water-Clocks and Time Measurement in Classical Antiquity|journal=Endeavour|volume=3|issue=1|year=1979|page=33|doi=10.1016/0160-9327(79)90007-3}}</ref> Slightly later, in the early 3rd century BC, the [[Hellenistic]] physician [[Herophilos]] employed a portable clepsydra on his house visits in [[Alexandria]] for measuring his patients' pulse-beats. By comparing the rate by age group with empirically obtained data sets, he was able to determine the intensity of the disorder.<ref name="John G. Landels 32"/>

Between 270 BC and AD 500, [[Hellenistic civilization|Hellenistic]] ([[Ctesibius]], [[Hero of Alexandria]], [[Archimedes]]) and [[Ancient Rome|Roman]] [[horology|horologists]] and [[astronomer]]s were developing more elaborate mechanized water clocks. The added complexity was aimed at regulating the flow and at providing fancier displays of the passage of time. For example, some water clocks rang [[bell (instrument)|bell]]s and [[gong]]s, while others opened doors and windows to show figurines of people, or moved pointers, and dials. Some even displayed [[astrology|astrological]] models of the universe. The 3rd century BC engineer [[Philo of Byzantium]] referred in his works to water clocks already fitted with an escapement mechanism, the earliest known of its kind.<ref>{{Harvnb|Lewis|2000|pp=356f.}}</ref>

The biggest achievement of the invention of clepsydrae during this time, however, was by Ctesibius with his incorporation of gears and a dial indicator to automatically show the time as the lengths of the days changed throughout the year, because of the temporal timekeeping used during his day. Also, a Greek astronomer, [[Andronicus of Cyrrhus]], supervised the construction of his Horologion, known today as the [[Tower of the Winds]], in the [[Athens]] marketplace (or [[agora]]) in the first half of the 1st century BC. This [[octagon]]al [[clocktower]] showed scholars and shoppers both [[sundial]]s and a [[windvane]]. Inside it was a mechanized clepsydra, although the type of display it used cannot be known for sure; some possibilities are: a rod that moved up and down to display the time, a water-powered [[automaton]] that struck a bell to mark the hours, or a moving star disk in the ceiling.<ref>{{cite journal |last1=Noble |first1=Joseph V. |last2=de Solla Price |first2=Derek |title=The Water Clock in the Tower of the Winds |journal=American Journal of Archaeology |date=October 1968 |volume=72 |issue=4 |pages=345–355 |doi=10.2307/503828 |jstor=503828 |url=https://www.jstor.org/stable/503828 |access-date=19 June 2024|url-access=subscription }}</ref>