Transit Of Venus Across The Sun

For the 1769 transit, scientists traveled to Hudson Bay (Canada), San José del Cabo (Baja California, then under Spanish control), Tahiti, and Norway. The Czech astronomer Christian Mayer was invited by Catherine the Great to observe the transit in Saint Petersburg with Anders Johan Lexell, while other members of Russian Academy of Sciences went to eight other locations in the Russian Empire. In Philadelphia, the American Philosophical Society erected three temporary observatories and appointed a committee, of which David Rittenhouse was the head. The results of these observations were printed in the first volume of the Society's Transactions, published in 1771.
Observations were also made from Tahiti at a location still known as "Point Venus". This occurred on the first voyage of James Cook, after which Cook explored New Zealand and Australia.
The unfortunate Guillaume Le Gentil spent eight years travelling in an attempt to observe either of the transits. His unsuccessful journey led to him losing his wife and possessions and being declared dead (his efforts became the basis of the play Transit of Venus by Maureen Hunter).
Unfortunately, it was impossible to time the exact moment of the start and end of the transit because of the phenomenon known as the "black drop effect". This effect was long thought to be due to Venus' thick atmosphere, and initially it was held to be the first real evidence that Venus had an atmosphere. However, recent studies demonstrate that it is an optical effect caused by the smearing of the image of Venus by turbulence in the Earth's atmosphere or imperfections in the viewing apparatus.