Twelve-inch quadrant, c 1767.

Twelve-inch quadrant, c 1767.
4 0 c m
actual image size: 23cm x 32cm


Quadrant made by John Bird, said to have been used by Captain James Cook (1728-1779). Astronomical quadrants were used to measure the angle of a celestial object from the zenith. Operated in conjunction with a transit instrument, they could be used to check the running rate of astronomical clocks known as regulators. At sea, a quadrant can be used to help fix a ships position and to determine latitude.

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© Science Museum / Science & Society Picture Library

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