The birth of scientific expeditions under the reign of Louis XIV of France: a case study

In the ambitious plan of King Louis XIV, better known as the Sun King, France should have become culturally dominant in Europe. To create this sort of a “golden age” for his country, the King thought he should have conquered and annexed the largest number of key territories through military campaigns. The First Minister of State Jean Baptiste Colbert suggested him to finance also scientific expeditions aimed to determine, with the highest possible accuracy, the extension of French colonial possessions, as that was the right way to show that France was the strongest and largest European power. The astronomers of the Académie des Sciences (founded in 1666), being also geographers and cartographers, were the “leading actors” of those dangerous expeditions, as measuring the terrestrial coordinates (latitude and longitude) strongly required their skills: in this way, the desire for glory of the Roi Soleil had unexpectedly turned out into an improvement of astronomy. All the expeditions were supervised by the Italian astronomer Giovanni Domenico Cassini (1625, Perinaldo - 1712, Paris) who had been warmly welcomed at the court of the Sun King in 1669 and was living in the Observatoire Royal de Paris. Cassini instructed the scientists who would have taken part to the expeditions, checked their instruments, and compiled a list of instructions concerning the observations they should have carried out. Among the several expeditions organized by Cassini, the 1672-73 one to Cayenne (French Guiana) deserves particular attention as thanks to observations carried out there by Jean Richer, Cassini obtained a value for the Earth-Sun distance (137.592.200 km) remarkably close to the real one (149.597.871 km) and unveiled the real size of the solar system. That was the first accurate measurement of the Earth-Sun distance but despite that, unexpectedly that extraordinary result appears to have been almost forgotten. Through a careful check and inspection of the available original documents kept in the Archives of the Académie in Paris, the history of the Cayenne expedition and of the observations which were carried out there, can be reconstructed and analyzed in detail. The aim of the project is to try to go back in the past to perceive the atmosphere of an epoch in which, thanks also to the overseas expeditions, began to bloom what it was going to become the Age of Enlightenment.