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Hadley's Quadrant
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octant

instrument

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navigational technology

  • officer using charts for navigation
    In navigation: Latitude measurements

    …even after 1731 when the octant (an early form of the modern sextant) was demonstrated independently by John Hadley of England (see photograph) and Thomas Godfrey of Philadelphia. In the octant and the sextant, two mirrors—one fixed, the other movable—bring the image of the Sun into coincidence with the horizon.…

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  • International Space Station
    In history of technology: Transport and communications

    …improved by conversion to the octant, using mirrors to align the image of a star with the horizon and to measure its angle more accurately: with further refinements the modern sextant evolved. Even more significant was the ingenuity shown by scientists and instrument makers in the construction of a clock…

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