in the pursuit of the Longitude Prize. A compromise was reached in which the monitoring of the Harrison mechanism was undertaken by Maskelyne and Green on alternate days. Green's return to England in the autumn of 1764 coincided with the death of Nathaniel Bliss; Green returned to Greenwich to continue Bliss' work until the appointment of a new Astronomer Royal. The new Astronomer Royal proved to be Nevil Maskelyne. Green briefly served under him as assistant, but left Greenwich after a disagreement with his new superior. Wales' account says that Green was involved in a survey to determine the feasibility of transporting water from the River Colne to provide water to Marylebone in London, although Green's survey confirmed the fears of mill owners downstream that the canal would result in a failure of the water supply needed for their operations and led to the scheme being dropped. Although this is unmentioned in Wales's short biography, Green is recorded as being the purser on HMS Aurora in 1768. In that same year, the Royal Society appointed him to accompany James Cook's voyage to observe the 1769 transit of Venus; despite their earlier disagreement, Maskelyne who was serving on the Society's Transit of Venus Committee recommended his former assistant for the post. Voyage of the Endeavour and the Transit of Venus Green joined Cook's first voyage of circumnavigation in 1768, accompanied by a servant. Green was one of two official astronomers appointed by the Royal Society to observe the transit; the other was Cook himself, who was a capable observer in his own right. Green was to receive 200 guineas from the Society for the appointment. (Cook was to receive 100 guineas for his role in making the observations.) The Society provided instruments for the expedition, including two reflector telescopes built by James Short, two clocks and an astronomical quadrant; these were supplemented by a telescope in the possession of Daniel Solander and another provided by the Navy. The expedition arrived at Tahiti, the chosen site for the observation of the transit, on 11 April 1769, anchoring in Matavai Bay on the north-western coast of the island two days later. A camp (Fort Venus) was established and the astronomical equipment was in place by the start of May. Of paramount importance for Green was the calculation of an accurate position of the location, which he calculated using the lunar distance method and