Bougner, PIERRE, a great French physicist, born at Croisic, in Brittany, 16th February 1698. In 1735 he was sent with Godin, La Condamine, and
Jussieu to South America to measure a degree of the meridian at the equator. During their seven years' absence Bouguer and his companions made valuable observations on the length of the seconds pendulum at great elevations, the deviation of the plumb-line from a vertical position through the attraction of a neighbouring mountain, the limit of perpetual snow, the obliquity of the ecliptic, &c. He published an account of his labours in the Théorie de la Figure de la Terre (1749). His investigations concerning the intensity of light laid the foundation of photometry; their results were fully embodied in his Traité d'Optique (1760). In 1748 Bouguer invented the héliometer, afterwards brought to greater perfection by Fraunhofer. He died at Paris, August 15, 1758.