James Cook’s very first voyage to the Pacific in 1768 was funded by the Royal Society with the express purpose of observing the Transit of Venus from Tahiti.
The idea of observing the transit from different places came from Sir Edmund Halley, the second Astronomer Royal.
In 1716, he suggested that if viewed simultaneously from different points on the globe, the transit could be used to determine the distance of the Earth from the Sun and so (with the help of Kepler’s equations) find the size of the Solar System.
In 1761 the Royal Society sent the astronomers Nevil Maskelyne (later the 5th Astronomer Royal) and Robert Waddington to St Helena, and Charles Mason and Jeramiah Dixon to the Cape of Good Hope. Unfortunately, bad weather ruined the observations of Maskelyne and Waddington, so a comparison between the two observations could not be made.
In 1769 the Royal Society funded and organised a new set of expeditions. This time, astronomers were sent to Hudson Bay, Cornwall, Ireland, Norway and Tahiti in the Pacific, to observe the second Transit of Venus that century. Lieutenant James Cook was chosen to command the expedition to Tahiti.