Valentin Haüy was his younger brother. Daubenton taught and encouraged him. Lamarck was friend as well as fellow-academician: they started a short-lived journal together. Lagrange, Laplace, Fourcroy, Berthollet, Malus and Legendre were colleagues at the Académie des Sciences. Geoffroy, a colleague and former pupil, interceded to have him freed from imprisonment during the Revolution (Haüy had to be persuaded to leave). He himself tried unsuccessfully to get Lavoisier freed (together they had earlier determined the weight of the kilogram). A suggestion of Coulomb’s led to his work on piezoelectricity.