Twelve inch portable astronomical quadrant, 1760-1769.
4 0 c m
 
31cm
actual image size: 23cm x 32cm

Twelve inch portable astronomical quadrant, 1760-1769.

© Science Museum / Science & Society Picture Library

Description

This portable astronomical quadrant was made in London by the famous English instrument maker John Bird (1709-1776). It was sent with one of the expeditions dispatched by the Royal Society to measure the 1769 transit of Venus. Captain Cook (1728-1779), who observed the event from Tahiti on his first voyage to the South Pacific (1778-81), may have even used this particular instrument. An astronomical quadrant was employed to measure the angle of a celestial object from the zenith. Objects were sighted using a pivoting telescope fitted with cros-hair wire that moved along a radial scale graduated in degrees. The instrument's orientation in both the horizontal and vertical could be finely adjusted using the plumb bob and spirit level.
 

Image Ref.

10196603
 

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