The Bureau des longitudes invested an astronomer at the Observatory, Alexis Bouvard (1767-1843), with the task of calculating new ephemeris tables for the giant planets. Everything worked out well for Jupiter and Saturn, but Uranus did not conform to predictions. Bouvard thought that its motion must have been perturbed by the attraction of an as yet unknown planet, situated beyond Uranus. This idea led Urbain Le Verrier (1811-1877) to discover in 1846 this new planet: Neptune, the last planet of the Solar System.

caption : Bouvard’s portrait - credits : Observatoire de Paris