In 1751, in conjunction with N. L. Lacaille, he measured the Moon’s distance. He helped organize expeditions to observe the transits of Venus in 1761 and 1769, and used the results to calculate the solar parallax. In 1801 he published Histoire céleste française, which contained a catalogue of over 47 000 stars. One of these ’stars’ was Neptune, which he recorded in 1795, 51 years before it was found by J. G. Galle.