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A 17th C. version of a simple quadrant missing its plumb bob, but with the two sighting pinholes clearly in evidence at the apex and to the right. This example represents the late evolutionary period of such instruments. It is engraved brass whereas earlier versions were of wood and it performs several functions which the earliest quadrants did not. The upper portion is engraved with a "shadow square" for use as a sundial. At the bottom it is divided to single degrees to allow for sighting the altitude of the sun or stars. Across the face of the instrument is a depiction of the celestial hemisphere showing major stars, the Equator, and Tropic of Cancer. Below these are engraved the months of the year, accounting for seasonal changes in the sun's declination and providing a Zodiacal calendar. This form of quadrant was also known as a "Gunter quadrant" after Edmund Gunter who described it in 1623.
This ingenious device was first proposed by English captain John Davis in 1594. The name "quadrant" came from the fact that 90° (or one quarter of a circle) could be measured even though there was no full 90° arc on the instrument. The backstaff consisted of two triangular arcs, the larger of which was calibrated to 30° and the one at the apex of the instrument which was calibrated to 60°.
French reflecting circle of brass with inlaid silver scale divided from 0 to 180 degrees on either side of the zero point.
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© 2008 USCG Lightship Sailors Association International Inc. Larry Ryan, President
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