In five sections with one on each of the five expeditions dispatched to observe the transit from Hawaii, Egypt, the island of Rodriguez, Kerguelen Island and New Zealand.
In 1716 Edmund Halley suggested that differences in the observations of the transit of Venus from opposite ends of the Earth would enable an estimate to be made of the distance of the earth from the sun and also therefore provide a measure of the size of the solar system. The first such measurements were made on a pair of transits in 1761 and 1764 and a reasonably accurate figure was arrived at. The next transit was in 1874 and provided an opportunity to significantly improve on the earlier measurements.