antik.it/Nautical-antiques/8114-Octant/
Code 8114
EUR 1800.00
In stock
1743174857Code 8114 OctantEbony 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 in wood and brass.
Measurements cm 25x30x8 – inches 9.8x11.8x3.1.
The octant, eighth part of the circle, is a reflecting instrument, proposed for the Western world around 1731 by John Hadley (1682-1744) and used to measure the height of the Sun or a star above the horizon at sea. A movable arm, equipped with a mirror and hinged on a graduated arc, allows the image of the star to be obtained by reflection superimposed on that of the horizon observed directly. The first instruments were made of fine wood, generally ebony or mahogany, and had ivory graduations; later they were replaced by brass or bronze instruments, while the graduation was engraved on a silver strip embedded in the metal arc of the limb. The need to make angle measurements more accurate required increasingly precise instruments and at the end of the seventeenth century the first document appears that mentions the principle of reflection of flat mirrors, applied to the measurement of angles, in this document an instrument invented around 1665 by Robert Hooke (1635-1703) and presented to the scientific community is mentioned. This instrument, being equipped with only one mirror, allowed for simple reflection and was therefore inadequate for the purpose.
Hooke realized the problem, but was unable to perfect his instrument; however, the idea of using reflection was taken into consideration by other researchers who studied how to correct the problems of the initial instrument, until in 1731, John Hadley presented his double reflection octant to the Royal Society of London, formed by a 45° arc, divided into 90 half degrees.
In 1732, the British Admiralty made the yacht Chatman available to test Hadley's instrument at sea, which received the praise of the most illustrious astronomers of the time.
The first instruments were made of fine wood, generally ebony, and had ivory graduations; they were later replaced by brass or bronze instruments, while the graduation was engraved on a silver strip embedded in the metal arch of the limb.
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Nautical antiques
Code 8114 Octant
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