Accession No
1646
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 and one other); metal (brass); ivory; glass
Dimensions
box length 330mm; breadth 295mm; height 90mm
Special Collection
Provenance
Donated in 01/1973.
Inscription
‘Spencer Browning & Co LONDON’ (ivory plate on brace)
‘S.B.R.’ (scale)
Description Notes
Ebony frame, ivory scale. Brass index arm with ivory, type-B vernier and clamp. Brass mounts for mirrors, shades and pinhole sights. Adjustable index mirror with three shades, adjustable horizon glass, two alternative pinhole sights. Inset ivory plate with maker’s inscription. Three brass feet. Pencil hole in brace. Note plate missing.
Keystone wooden box.
Condition unacceptable; incomplete (tangent screw, pencil and note plate 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:42764
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