Digital Rare Book:
Voyage dans les mers de l'Inde
Fait par ordre du roi, à l'occasion du passage de Vénus, sur le disque de soleil, le 6 juin 1761, & le 3 du même mois 1769.
By Guillaume Joseph Hyacinthe Jean Baptiste Le Gentil De La Galaisière,
Published 1779 by De l'imprimerie royale in Paris .
Written in French.

The Ordeal of Guillaume Le Gentil
By Michael Wright

Does this scenario sound familiar? You buy a new piece of gear; say an eyepiece that you are dying to try out on your favorite deep sky object. It arrives in the mail on a weekday so you decide wait until the week-end. On Saturday, Clear Sky Chart predicts above average seeing and transparency, but as you are pulling out your scope, your spouse reminds you that your child has a recital that evening. You do the right thing and put the scope back.

Next time your observing plans are frustrated, take consolation in the story of Guillaume Le Gentil. In 1760, Le Gentil was commissioned by the French Academy of Sciences to observe the 1761 transit of Venus from Pondicherry, India. Sailing from France in March 1760, he arrived on the Isle de France (Mauritius) in July where he learned that war had broken out between France and Britain preventing further passage east. In February 1761, he was finally able to secure passage. Despite the upcoming monsoon season, he was assured that he could reach Pondicherry by mid-April in plenty of time for the transit on June 6. Unfavorable winds blew his ship off course, so it spent five weeks wandering around the Indian Ocean and the Arabian Sea. Upon nearing Mahé on the west coast of India, the captain learned that Pondicherry had been captured by the British so he decided to return to Isle de France. Le Gentil had no choice but to remain on board for the return trip. On the day of transit, Le Gentil was on board ship and unable to make accurate observations on the rolling deck.

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The Wiki interestingly has this to say:

One of his interesting findings was that the duration of the lunar eclipse of 30 August 1765 was predicted by a Tamil astronomer, based on the computation of the size and extent of the earth-shadow (going back to Aryabhata, 5th c.), and was found short by 41 seconds, whereas the charts of Tobias Mayer were long by 68 seconds

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