Back-staff, or Back quadrant [in Navigation]

Back-staff, or Back quadrant [in Navigation]

an Instrument by the French, called the English Quadrant, invented by Captain Davis: Being the simplest and exactest Instrument hitherto invented for taking the Sun’s Zenith Distance at Sea, by the Help of which the Latitude is presently known.

It consists of two Arches, the Arch x of the least Radius contains 60 degrees, and that of y having the largest Radius contains three Degrees. It has also three Vanes; the Vane at h is called the Horizon Vane, that at S the Shadow Vane, and the Vane at E is called the Sight Vane.

Definition taken from The Universal Etymological English Dictionary, edited by Nathan Bailey (1736)

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