Accession No
1161
Brief Description
octant, attributed to John Rutledge, English, c. 1770
Origin
England
Maker
Rutledge, John [attributed]
Class
navigation
Earliest Date
1770
Latest Date
1770
Inscription Date
Material
wood (mahogany); metal (brass); ivory; glass
Dimensions
Special Collection
Provenance
Possibly belonged to Prof. A. Hutchinson in 1937 (as indicated by R.T. Gunther, Early Science in Cambridge).
Inscription
‘*Iohn Rutledge*’
Description Notes
Mahogany frame, ivory scale. Mahogany and brass index arm with ivory, A-type vernier and brass clamp. Brass mounts for mirrors and shades. Adjustable index mirror with two shades. Horizon glass with lever adjustment. Brass double pinhole sight. Backsight and back horizon glass with lever adjustment. Hole for shades. Ivory inset plate for maker’s or owner’s name. Note plate missing. Hole in brace for pencil. Three brass feet.
Condition good; incomplete (note plate 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:39660
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