Simone Dumont and Monique Gros
Joseph-Nicolas Delisle, as a member of the Académie Royale des Sciences of Paris and professor at the Collège Royal de France, went to England in 1724 to visit Newton and Halley. The latter suggested observations of the transits of Mercury and of Venus in order to obtain the solar parallax. Delisle was also interested in the Mercury transits. After a stay of 22 years in Saint Petersburg, on his return to Paris, he distributed avertissements (information bulletins) encouraging all astronomers to observe the same phenomena, like the solar eclipse of 1748. Later, in 1760, Delisle presented an Adresse to the King and to the Académie in which he detailed his method to observe the 1761 transit of Venus. This was accompanied by a mappemonde showing the best places for observations. Copies of the text, together with 200 maps, were sent to his numerous correspondents in France and abroad.
Following the advanced age and finally death of Delisle, his assistant and successor Joseph-Jérôme Lalande presented a mémoire related to the 1769 transit of Venus and an improved map of the best observing places. We detail the role of Delisle and Lalande in the preparation of the international collaboration related to these two transits.
Manuscript: jad19_1n.pdf