Accession No
0056
Brief Description
octant, by Spencer, Browning and Company, English, 1850 (c)
Origin
England; London
Maker
Spencer, Browning and Company
Class
navigation
Earliest Date
1850
Latest Date
1850
Inscription Date
Material
wood (ebony, mahogany); ivory; metal (brass); glass
Dimensions
box length 276mm; breadth 262mm; height 105mm
Special Collection
Robert Whipple collection
Provenance
Purchased by Robert Stewart Whipple in Brussels in 08/1922.
Inscription
‘SPENCER BROWNING & CO LONDON
SOLD BY SELBY. PORTSMOUTH’
Description Notes
Ebony frame, ivory scale. Reinforced brass index arm with ivory, B-type vernier, brass clamp and tangent screw. Brass mounts for mirrors and shades. Adjustable index mirror with three shades. Horizon glass with lever adjustment (centre screw missing) moved by knurled screw. Square for adjusting plane of horizon glass. Two shades for horizon glass. Alternative brass-mounted pinhole and telescopic sights. Inset ivory plate for maker’s inscription. Inset ivory note plate. Two brass feet (one broken off). Hole in brace for pencil.
Fitted mahogany box.
Condition: fair; incomplete (centre screw, one foot and pencil missing)
References
Events
Description
John Hadley, an English seafarer, invented the octant (also called a Hadley quadrant) during the 1730’s. It was used to find latitude by measuring the altitude of the sun, moon or stars.
An octant is an angle of 45°, or an eighth of a circle. The octant was first made with mahogany frames and scales on inlaid boxwood. By the early 19th century ebony (a much more hard wearing wood) had replaced the mahogany to craft the frames which had brass index arms.
The octant is used in a similar way to a sextant. The observer raises the octant until the horizon can be seen through the horizon glass. The index arm and attached index glass are moved until the twice-reflected image of the sun or star can be seen superimposed on the horizon, enabling an angle to be read off.
The octant was inexpensive and became the everyday instrument for measuring latitude, whilst the more expensive sextant was used to find longitude by measuring lunar distances.
Created by: Corrina Bower
FM:39678
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