Jean Nicolas Pierre, an eminent French geometer, was born at Mezieres, May 6, 1769 or 1770. His father was a barber, and without the means of educating his son. The genius of the youth, however, was speedily re- cognised by Monge, then living at Mezieres. By his kind- ness the young Hachette was sent to the university of Reims, where he studied so successfully, that at the age of twenty- three he defeated all his fellow candidates in the concours for the professorship of hydrography at Collioure and Port- Vendre. When the polytechnic school was opened in 1794, Hachette was attached to the professional staff, with the de- partment of descriptive geometry, and trained some of the very best geometers of his age and country, such as Pois- son, Arago, Fresnel, and many others. He held this office till the restoration of the Bourbons, who deprived him of it and expelled him from the Institute. The Revolution of 1830 reinstated him in his offices and honours, of which he retained peaceful possession till his death, four years later, Jan. 16, 1834. Hachette's character as a man stood as high as his scientific fame. His personal worth was of that solid and unostentatious kind, more common in England than in France, though appreciated quite as fully in the latter as in the former country. His high sense of duty, his simplicity, and his quiet benevolence, endeared him to all who enjoyed the privilege either of his instructions or of his private friendship. His services to science lay chiefly in the field of descriptive geometry, with which he was pro- foundly acquainted, both in its theory and its practical ap- plication to the arts, especially in the construction of ma- chinery. To him is due the merit of having given to machinery that impulse, in virtue of which France has in that department advanced so rapidly and so far since his day.

Hachette's principal works are his Deux Supplementes à la Géomé- trie Descriptive de Monge, 1811 and 1818 respectively; Éléments de Géométrie à Trois Dimensions, Paris, 1817; Collection des Épreuves de Géométrie à Trois Dimensions, &c., 1795 and 1817; Applications de Géométrie Descriptive, Paris, 1817; Traité de Géométrie Descriptive, &c., Paris, 1822; Traité Élémentaire des Machines, Paris, 1817; Correspondance sur l'Ecole Polytechnique, 1804-1818. Hachette also contributed many valuable papers to the leading scientific journals of the day.