BOUGTJER, PIERRE (1698-175S). A French mathematician and physicist, the founder of photometry. He was born at Croisic, in Bretagne, and studied in the Jesuit College at Vannes. In 1713 he succeeded his father as professor of hydrography in Croisie, whence he removed to a similar office in Havre in 1730. In 1729 he published his Essai d'optique sur hi graduation do la lumierc. In 1731 he was made associate geometer of the Academy of Sciences, and was promoted to the office of pen sioned astronomer in 1735. In that year also he was chosen to proceed. along with Galin. La Condamine, and Jussieu, to South America. for the purpose of measuring a degree of the merid ian at the equator. They had to contend with many difficulties, and were more than seven years away from home, during which time Bouguer made valuable observations on the length of the seconds pendulum at great elevations. the devia
tion of the plumb line from a vertical position through the attraction of neighboring mountains, the line of perpetual snow, etc. He published an account of his labors and those of his colleagues in a magnificent work, entitled Theorie do In figure de in terse (Paris. 1749). Bouguer's in vestigations concerning the intensity of light laid the foundation of photometry; and their results. which had been partly exhibited in the optical work already noticed, were more fully em bodied in his Traits d'optique say In gradua tion de la lumiere, which was edited after his death by Laeaille (1760). Ile is the inventor of the heliometer (q.v.). Ile published an excellent :Vol/Mill trait(' de narigatio• et de pilotage (1753), and numerous works in the Memoires de l'Aeademie des Sciences (1726 to 1757).