Accession No
0050
Brief Description
octant, by B. Messer, English, 1790 (c)
Origin
England; London
Maker
Messer, B.
Class
navigation
Earliest Date
1790
Latest Date
1790
Inscription Date
Material
wood (mahogany and one other); ivory; metal (brass); glass
Dimensions
box length 475mm; breadth 400mm; height 93mm
Special Collection
Robert Whipple collection
Provenance
Purchased by Robert Stewart Whipple in Sheffield in 07/1922.
Inscription
‘B: MESSER LONDON’
‘No 1’ (ms label in box)
Description Notes
Octant, by B. Messer, English, c. 1790.
Mahogany frame, ivory scales. Brass index arm with ivory, type-B vernier and brass clamp. Brass mounts for mirrors and shades. Adjustable index mirror with three shades. Backsight (single pinhole) and back horizon glass with lever adjustment. Inset ivory plate with maker’s inscription. Ivory note plate on reverse. Three brass feet. Pencil with ivory cap screwed into frame.
Step wooden box with key.
Condition: good; complete
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:39655
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