74

The discovery of the planet Neptune in 1846 based on the theoretical calculations of Urbain Le Verrier is nowadays seen as an outstanding event. However, it is more rarely pointed out that the Paris Observatory was not itself able to carry out telescopic investigations of the new planet. This fact deserves to be highlighted as it is indicative of a significant lag in French astronomy with regard to its German, English and Russian counterparts.This discovery is also one of the greatest achievements of a new type of astronomy, the « astronomy of the invisible » founded by Friedrich Wilhelm Bessel. It is a harbinger of major changes in the methods and objects of astronomy. However, whilst it enshrines the dogma of Newtonian gravitation, it also constitutes the main obstacle to the development of physical astronomy, of which François Arago was one of the key precursors.