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Davis' Quadrant

The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the sun or moon. When observing the sun, users kept the sun to their back and observed the shadow cast by the upper vane on a horizon vane. It was invented by the English navigator John Davis who described it in his book Seaman's Secrets in 1594. The quadrant was the earliest astronomical instrument converted for nautical use. It was used to determine the altitude of the Polestar or sun and, concurrently, the location of the ship in degrees of latitude.
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Title:
Davis' Quadrant
Caption:
The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the sun or moon. When observing the sun, users kept the sun to their back and observed the shadow cast by the upper vane on a horizon vane. It was invented by the English navigator John Davis who described it in his book Seaman's Secrets in 1594. The quadrant was the earliest astronomical instrument converted for nautical use. It was used to determine the altitude of the Polestar or sun and, concurrently, the location of the ship in degrees of latitude.
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Credit:
Album / Science Source / New York Public Library
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Image size:
4800 x 3283 px | 45.1 MB
Print size:
40.6 x 27.8 cm | 16.0 x 10.9 in (300 dpi)
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