Old instruments
Hadley Quadrant
Direct answer
Hadley Quadrant is an early double-reflection instrument associated with John Hadley's octant design.
Hadley Quadrant is an early reflecting octant used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Octant, Reflecting Circle, Mariner's Astrolabe, Equinoctial Ring Dial
Hadley Quadrant is an early reflecting octant 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 Hadley Quadrant
Hadley's eighteenth-century reflecting design was a decisive step toward the modern marine sextant.
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Why Hadley Quadrant matters
Hadley Quadrant matters because it allowed a navigator to hold the horizon and a reflected body in one field while reading a stable angle.
How to read Hadley Quadrant
Read Hadley Quadrant by checking mirror alignment and using the index arm to superimpose the target on the horizon.
Hadley Quadrant in practice: an example
A star altitude could be observed even while the instrument moved with a ship.
Where readings of Hadley Quadrant go wrong
Historical names overlap: many so-called Hadley quadrants are octants, so identify the actual arc and construction.
Sources and editorial method
Research references used for this entry include:
- Royal Museums Greenwich: Astronomical and Navigational Instruments - Museum reference collection for historical observing, calculating, timekeeping, and navigation instruments.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
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More in Historical Almanacs & Instruments
- Lunar Distance Table
- Plumb Line
- Sextant
- Volvelle
- Assumed Position
- Celestial Navigation
- Declination Table
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Common questions
What is a hadley quadrant?
Hadley Quadrant is an early double-reflection instrument associated with John Hadley's octant design.
What do people get wrong about a hadley quadrant?
Historical names overlap: many so-called Hadley quadrants are octants, so identify the actual arc and construction.
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