Accession No
0596
Brief Description
octant, c.1795
Origin
England
Maker
Class
navigation
Earliest Date
1795
Latest Date
1795
Inscription Date
Material
wood (ebony and one other); metal (brass); ivory; glass
Dimensions
box length 420mm; breadth 370mm; height 100mm
Special Collection
Robert Whipple collection
Provenance
Purchased from T.H. Court on 01/03/1930.
Inscription
‘*B. Liefringh * 1795’ (octant - probably first owner)
‘B. LIEFRINGH 1795’ (box)
Description Notes
Ebony frame, ivory scale. Brass index arm with ivory, type-B vernier and brass clamp. Brass mounts for mirrors and shades and brass double pinhole sight. Adjustable index mirror with three shades. Horizon glass with lever adjustment. Ivory inset plate with owner’s (?) name. Ivory inset note plate on reverse. Three brass knurled feet. Pencil with ivory cap screwed into brace.
Step wooden box.
Condition good; complete.
References
Events
Description
John Hadley, an English seafarer, invented the octant (also called a Hadley quadrant) during the 1730s. 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:39657
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