John, an able mathematician, and one of the most learned astronomers of the seventeenth century, was born at Flèche, and became priest and prior of Rillé in Anjou. Going to Paris, he was in 1666 received into the Academy of Sciences in quality of astronomer. In 1671, he was sent, by order of the king, to the castle of Uraniburg, built by Tycho Brahe, in Denmark, in order to make astronomical observations there; and thence he brought the original manuscripts written by Tycho Brahe, which are of the greater value as they differ in many places from the printed copies, and contain a book more than has yet appeared. He made important discoveries in astronomy, and was the first who travelled through several parts of Picardy, France to measure a degree of the meridian. His works are, 1. A Treatise on Levelling; 2. Fragments of Dioptrics; 3. Experimenta circa Aquas effluentias; 4. De Mensuris; 5. De Mensura Liquidorum et Aridorum; 6. A Voyage to Uraniburg, or astronomical observations made in Denmark; and, 7. Astronomical Observations made in several parts of France. These, and some other of his pieces, are contained in the sixth and seventh volumes of the Memoirs of the Academy of Sciences.