Old instruments
Clepsydra
Direct answer
Clepsydra is a device that measures time through the controlled flow of water into or out of a vessel.
Clepsydra is a water-flow timekeeper used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Regulator Clock, Pendulum Clock, Water Clock, Hourglass
Clepsydra is a water-flow timekeeper used in historical astronomy, timekeeping, or navigation.
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The story behind Clepsydra
Water clocks appeared in several ancient cultures and supported civic, ritual, and observational timing.
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Why Clepsydra matters
Clepsydra matters because it allowed timed intervals without relying on direct sunlight.
How to read Clepsydra
Read Clepsydra by reading the scale or mechanism while accounting for head pressure, temperature, and flow consistency.
Clepsydra in practice: an example
An observer can time an interval by the change in water level between marked graduations.
Where readings of Clepsydra go wrong
Flow is not automatically uniform, so a simple vessel should not be assumed to measure equal hours accurately.
Sources and editorial method
Research references used for this entry include:
- Royal Museums Greenwich: A Unique History of Timekeeping - Museum overview of marine chronometers, astronomical regulators, and the development of precision timekeeping.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
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Common questions
What is Clepsydra?
Clepsydra is a device that measures time through the controlled flow of water into or out of a vessel.
What do people get wrong about Clepsydra?
Flow is not automatically uniform, so a simple vessel should not be assumed to measure equal hours accurately.
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