image astronomical quadrant RS_63 pic1
Image number: RS.8471
Credit: © The Royal Society
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Astronomical quadrant


ca. 1767


John Bird (1709-1776, British), Instrument maker

Object type



Content object


A 12-inch astronomical quadrant made by John Bird.

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 ship's position and to determine latitude.

Object history

This quadrant is said to have been used by Captain James Cook during his observations of the transit of Venus in Tahiti.

Associated place

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