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OCTANT
OCTANT

OCTANT

DimensionsHt:8.50 x L:33.00 x W:27,00 x cm
Object numberHF.78.64.1
DescriptionBrass and hardwood octant; Frame shaped like isosceles triangle, with arc at base. Ivory inset along arc is graded from 0 degrees to 105 degrees. Frame stands on three brass legs. Index arm pivots at point of triangle; opposite end swings across graduated arc. Free end of arm flares to a square. Rectangular cut-out on square is faced on one side with a graded ivory inset allowing the measured angle to be read. Immediately above the index arm pivot is the index glass. The mirrored glass is set in a three-sided brass casing. The horizon glass is set on the octant's right radius and is half mirrored. Three horizon glass shades are hinged on the right radius, between the glasses. Circular pieces of red, dark red and green glass are set into square brass casings. An ivory inset reads "Spencer & Co., London"
Narrative
Octants were developed around 1730, almost simultaneously by two different men - English mathematician, John Hadley, and American glazier, Thomas Godfrey. Hadley obtained a British patent in 1734 so octants can also be known as Hadley quadrants.?

These portable instruments became popular with navigators and within 50 years of being invented, the octant superseded previous instruments. Octants were the 18th-century versions of GPS but with far more math! They were used to calculate the altitude of the Sun or other celestial objects above the horizon at sea. These measurements, used in combination with other data relating to the height of the Sun, could determine a ship's latitude.?

Eventually, octants were replaced by more accurate instruments like sextants, favoured by naval navigators. But octants remained in use well into the 19th century as they were a cost effective and popular instrument favoured by merchant and fishing fleets.