Advanced water clock (Ctesibius' clepsydra)
Reloj de agua de flujo constante con indicador (clepsidra de Ctesibio)
- Date
- c. 270 BCE · confidence medium
- Place
- Alexandria, Egypt
- Credited to
- Ctesibius of Alexandria
- Field
- Knowledge & symbols
What it is
A clepsydra with a constant-level reservoir (float valve) ensuring uniform flow, and a float that moves a pointer over a drum marked with hours. It was the most accurate clock until the medieval mechanical escapement.
Simple clepsydras existed in Egypt from c. 1500 BCE; the innovation is flow regulation.
What it led to
- Feedback control (level regulation), the first known feedback mechanism
- Uniform time measurement for astronomy, courts and watches
- Hydraulic automata and the Alexandrian water organ
- A tradition leading to Chinese (Su Song) and Arab astronomical clocks
Built on
- Water clock (clepsydra)c. 1500 BCE
- Gnomon and graduated sundialc. 560 BCE
- Athenian courtroom water clockc. 400 BCE
- Toothed gearc. 270 BCE
- Egyptian single-outflow water clock