This cased marine or naval sextant is a double reflection instrument used to measure the angle between any two visible objects. The name ‘sextant’ comes from the extent of its limb that is the sixth part of a circle. The main use of a sextant is to determine the angle between a celestial object and the base horizon, which defines the object’s altitude. The arc portion of this marine sextant is graduated into degrees from right to left, starting from 0 to 120.  Also engraved on the arc is the maker “Spencer & Co., London”. The firm was formed in 1784 and later changed to call “S.B.R.” where it was operational at 66 Wapping, London from 1839.

With a sextant, knowledge of the time and date with valid charts allows a navigator to determine his latitude or position on the surface of the earth or on the open seas. This English sextant is made of brass and consists of a frame or a wedge that spans 60 degrees, index mirror, telescope, index bar, magnifying glass, clamp, arc, seven shade glasses, and the horizon marker. Frame has a lathe-turned, wooden handle and three strong pins for resting the instrument in the case. Instrument is covered with surface grime and is missing a threaded brass lens piece for the magnifying glass. Comes with its original double-hinged wooden case screwed and dovetailed. Inside the case is a period paper label identifying the maker. Also has a set of calipers, two, brass portable screws-on lens devices and an old pasteboard tag.  In good condition.

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