Old instruments
Hourglass
Direct answer
Hourglass is a sealed pair of bulbs in which sand passes through a narrow opening to measure a fixed interval.
Hourglass is a sand-flow interval timer used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Clepsydra, Water Clock, Compass Rose, Magnetic Compass
Hourglass is a sand-flow interval timer used in historical astronomy, timekeeping, or navigation.
An engraved functional orientation; the page explains the real instrument, method, or publication.
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The story behind Hourglass
Sandglasses were used aboard ships and in workshops, churches, households, and scientific practice.
A one-minute story
The Book of the Sky
How people learned to read the sky, from Babylon to the day you were born.
Why Hourglass matters
Hourglass matters because its portable repeatability helped organize watches, observations, and short procedures without sky visibility.
How to read Hourglass
Read Hourglass by starting from a fully settled charge and turning it promptly at each completed interval.
Hourglass in practice: an example
A half-hour glass can mark segments of a ship's watch alongside course and speed records.
Where readings of Hourglass go wrong
Tilt, moisture, static, damaged grains, and late turning accumulate error over repeated intervals.
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.
- Royal Museums Greenwich: Traverse Board - Museum documentation of the peg board used to record a vessel's course and speed by watch.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
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Common questions
What is Hourglass?
Hourglass is a sealed pair of bulbs in which sand passes through a narrow opening to measure a fixed interval.
What do people get wrong about Hourglass?
Tilt, moisture, static, damaged grains, and late turning accumulate error over repeated intervals.
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