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An octant is a historical instrument used in navigation to determine the angle between a celestial body (such as the Sun, Moon, or stars) and the horizon. It was widely used by sailors and navigators in the 18th and 19th centuries for celestial navigation, which involves using the positions of celestial bodies to determine the ship's position and course.

The octant is a predecessor to the sextant, which is a similar instrument but with greater precision. The octant gets its name from the fact that the instrument's arc covers one-eighth of a circle (45 degrees). It consists of a graduated scale, called the arc, and a movable arm called the index arm or horizon bar, which carries a small mirror or prism called the index mirror. By adjusting the position of the index mirror, the navigator can align the image of a celestial body with the visible more... horizon and measure the angle between them.

The octant allowed navigators to determine their latitude and longitude at sea, which was essential for safe and accurate navigation. While the octant is no longer in common use, it remains an important historical artifact. less...

An antique ebony and ivory mariner's octant by Walker of London,…
1820 Walker London Mariner's Octant: Ebony and Ivory Antique

An antique ebony and ivory mariner's octant by Walker of London, dated 1820, 13.78 in. high

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An antique nautical octant by Spencer Barrett & Co, London,…
Antique Nautical Octant by Spencer Barrett & Co

An antique nautical octant by Spencer Barrett & Co, London, circa 1840with ivory inlay and brass fittings13.19 in. long

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A cased brass octant, by G. Heath, London, 19th century, a…
G. Heath Brass Octant with Fitted Case

A cased brass octant, by G. Heath, London, 19th century, a brass and ebony instrument with finely calibrated ivory plaque to vernier arc, maker's mark to an ivory cartouche between the two limbs, housed in a fitted case, with remnant label to interior of l

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Victorian ebonized & ivory inset octant by J. Kidd Dundee
Victorian Octant by J. Kidd Dundee

Victorian ebonized & ivory inset octant by J. Kidd Dundee

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19th century ebonised radius octant with ivory scale, engraved…
Ebonised Octant with Ivory Scale and Brass Arm

19th century ebonised radius octant with ivory scale, engraved brass index arm and ivory inset to the T plate (no makers name or case)

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19th century oak cased octant by Ripley & Son London, ivory…
Antique Oak Octant by Ripley & Son London

19th century oak cased octant by Ripley & Son London, ivory scale and brass index arm, makers name to ivory inset on T plate, in a stepped and stained oak box

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19th century oak cased radius octant by Norie & Co London with…
19th Century Norie & Co Oak Octant

19th century oak cased radius octant by Norie & Co London with ebonized T frame, ivory scale with vernier, makers name to ivory T plate, the lid of the box with paper label for D. McGregor & Co, Glasgow and Greenock, c1820-30

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A vintage brass pocket drum sextant, circa 1943, including a…
1943 Vintage Brass Pocket Drum Sextant with Octant Case

A vintage brass pocket drum sextant, circa 1943, including a brass octant case, the sextant cover reading 'Tp Wmc No.57 D^D', the largest 2.76 in. diameter

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A double T-Frame Octant, by Spencer Browning & Co., London,…
Antique Octant with Case and Accessories, London, 1840

A double T-Frame Octant, by Spencer Browning & Co., London, circa 1840, complete with all filters, sighting tubes and degree scale housed in a mahogany wedge-shaped case with paper label attached to interior lid 'G.B.H. Filbri Jr: {Amsterdam, Netherlands},

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Cased Octant by Peter Mc Millan, Aberdeen, late 19th century,…
Antique Octant in Mahogany Case

Cased Octant by Peter Mc Millan, Aberdeen, late 19th century, brass, timber and bone inlay, mahogany case, height 5.12 in., length 11.81 in., depth 12.99 in.

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14 inch radius ebony frame and limb octant by Spencer Browning…
Antique Ebony Octant by Spencer Browning & Rust, London (1810)

14 inch radius ebony frame and limb octant by Spencer Browning & Rust, London, circa 1810, ivory scale divided -2 to 99, brass index arm, ivory vernier divided 0-20, brass thumbscrew lock, sighting vane absent, brass mirrors and plug in shades (green, red

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10 inch radius rosewood or ebony frame and limb octant, ivory…
Antique Spencer Browning & Rust Octant

10 inch radius rosewood or ebony frame and limb octant, ivory plaque to crossbar marked 'Spencer Browning & Rust, London' (1784-1840), ivory scale divided -3 to 108, brass index arm, ivory vernier (chipped) divided 0-20, brass thumbscrew lock and adjustmen

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16 inch radius mahogany octant, marked Tobias Black on ivory…
18th Century Tobias Black Mahogany Octant

16 inch radius mahogany octant, marked Tobias Black on ivory plaque on the crossbar, with boxwood scale divided -2 to 99, mahogany and brass index arm, boxwood vernier scale divided 0-20, brass thumbscrew lock, brass sighting vane, mirrors, and shades (blu

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10 inch radius ebony frame and limb octant, c.1820, ivory…
Antique Ebony Octant with Ivory Plaque, London, c.1820

10 inch radius ebony frame and limb octant, c.1820, ivory plaque to crossbar later marked 'Cary London', replaced brass scale divided -1 to 93, brass index arm, ivory vernier (chipped) divided 0-20, brass thumbscrew lock and adjustment screw, sight vane ab

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10 inch radius ebony frame and limb octant, ivory plaque to…
Ebony Octant with Ivory Scale and Sight Vane

10 inch radius ebony frame and limb octant, ivory plaque to crossbar marked 'Josh Long, London', ivory scale divided -2 to 100, brass index arm, ivory vernier divided 0-20, brass thumbscrew lock and adjustment screw, two pinhole sight vane with swivel shut

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16 inch radius ebony frame and limb octant by Spencer Browning…
Antique Ebony Octant with Ivory Plaque, London 1794

16 inch radius ebony frame and limb octant by Spencer Browning & Rust, London, ivory plaque to crossbar marked 'Robert Robinson 1794', ivory scale divided -2 to 99, brass index arm, ivory vernier divided 0-20, brass thumbscrew lock, two pinhole sight vane

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9 inch radius ebony frame and limb octant, ivory plaque to…
Johannsen & Co. Ebony Sextant with Ivory Plaque

9 inch radius ebony frame and limb octant, ivory plaque to crossbar marked 'A. Johannsen & Co., 149 Minories, London', ivory scale divided -5 to 110, brass index arm, ivory vernier divided 0-20, brass thumbscrew lock and adjustment screw, screw in brass si

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12 inch radius ebony frame and limb octant by Spencer Browning…
Antique Ebony Octant by Spencer Browning & Rust

12 inch radius ebony frame and limb octant by Spencer Browning & Rust, London, (1784-1840), crossbar plaque absent, ivory scale divided -2 to 99, brass index arm, ivory vernier divided 0-20, brass thumbscrew lock, two pinhole sight vane with swivelling shu

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14 inch radius mahogany octant, marked 'Thomas Given 1803' on…
1803 Thomas Given Mahogany Octant with Accessories

14 inch radius mahogany octant, marked 'Thomas Given 1803' on ivory plaque on the crossbar, with ivory scale divided -2 to 99, black lacquered brass index arm engraved 'Gurden Salharp', ivory vernier scale divided 0-20, brass thumbscrew lock to back and sc

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An Austrian miniature brass octant, by G. Sadtler, Vienna, 19th…
Austrian Miniature Brass Octant with Case

An Austrian miniature brass octant, by G. Sadtler, Vienna, 19th century inscribed 'G. Sadtler in Wien', fitted wooden case 3.94 in. high

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A ship's octant, in mahogany case, English, late 19th century,…
19th Century English Mahogany Octant in Case

A ship's octant, in mahogany case, English, late 19th century, 11.02 in. high

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Vintage wood cased brass octant
Antique Brass Octant with Wooden Case

Vintage wood cased brass octant

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Antique ebony & brass octant 19th century, with ebony frame,…
19th Century Ebony and Brass Octant with Vernier Scale

Antique ebony & brass octant 19th century, with ebony frame, ivory inlay and Vernier scale, in timber box. No makers marks.

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A 19th century ebony octant by D. McGregor of Glasgow and…
Antique Ebony Octant by D. McGregor with Original Case

A 19th century ebony octant by D. McGregor of Glasgow and Greenock, brass fittings, ivory scale, original case, some attention required.

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