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Ebony, brass octant signed Hughes London made around 1830

About the Item

Ebony wood, brass and marine ivory octant, scale from 0° to 100°,signed Hughes London made around 1830. Good condition, complete with custom-made display base made of wood and brass. Measures 25x30x8 cm - inches 9.8x11.8x3.1. The octant, eighth part of the circle, is a reflection instrument, proposed for the Western world around 1731 by John Hadley (1682-1744) and used to measure at sea the height of the Sun or a star relative to the horizon. A movable arm, equipped with a mirror and pivoted on a graduated arc, makes it possible to obtain by reflection the image of the star superimposed on that of the directly observed horizon. Early instruments were made of fine wood, usually ebony or mahogany, and had ivory graduation; later they were replaced by brass or bronze instruments, and the graduation was engraved on a silver strip embedded in the metal arch of the flap. The need to make angle measurements more accurate required more and more precise instruments, and in the late seventeenth century the first document appears that mentions the principle of reflection of plane mirrors, applied to the measurement of angles, in this document an instrument is mentioned devised around 1665 by Robert Hooke (1635-1703) and presented to the scientific community. This instrument being equipped with only one mirror allowed for simple reflection and was therefore inadequate for the purpose. Hooke realized the drawback, but failed to perfect his instrument; however, the idea of making use of reflection was taken up by other researchers who studied ways to correct the drawbacks of the initial instrument, until in 1731, John Hadley presented his double-reflection octant, formed by a 45-degree arc divided into 90 half-degrees, to the Royal Society of London. In 1732, the British Admiralty made the yacht Chatman available to experiment in navigation with Hadley's instrument, which won praise from the most distinguished astronomers of the time. Early instruments were made of fine wood, usually ebony, and had ivory graduation; later they were replaced by brass or bronze instruments, and the graduation was engraved on a silver strip embedded in the metal arch of the flap.
  • Dimensions:
    Height: 11.8 in (29.98 cm)Width: 9.8 in (24.9 cm)Depth: 3.1 in (7.88 cm)
  • Materials and Techniques:
  • Period:
  • Date of Manufacture:
    1830
  • Condition:
    Wear consistent with age and use.
  • Seller Location:
    Milan, IT
  • Reference Number:
    1stDibs: LU1020244268932

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