Accession No

0746

Brief Description

octant, by Spencer, Browning and Rust, English, 1800 (c)

Origin

England; London

Maker

Spencer, Browning and Rust

Class

navigation

Earliest Date

1800

Latest Date

1800

Inscription Date

Material

wood (ebony and one other); metal (brass); ivory; glass; paper

Dimensions

box length 375mm; breadth 350mm; height 95mm

Special Collection

Robert Whipple collection

Provenance

Purchased from L.H. Spero, Harrow, England, on 25/01/1934. The catalogue card says: ‘A.R. Hall says formerly the property of Captain Ross (?), 1949 Cat. p.11’

Inscription

‘Spencer Browning and Rust London’ (ivory plate on brace)
‘SBR’ (scale)

Description Notes

Ebony frame, ivory scale. Brass index arm with ivory, type-B vernier and brass clamp. Brass mounts for mirrors and shades. Adjustable index mirror with three shades. Horizon glass with lever adjustment. Brass single pinhole sight. Backsight with two pinholes and back horizon glass with lever adjustment. Hole for shades. Inset ivory plate with maker’s inscription. Inset ivory note plate on reverse. Three brass feet. Pencil hole in brace.
Step wooden box with two trade labels and brass handle.

Condition fair (one mirror cracked); incomplete (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:39659