BOUGUF.R (PErsa), in biography, a celebrated French mathematician, born at Croisci, in Lower Bretagne, in Febru ary, 1698. His father, John, was profes sor of hydrography, and author of " A Complete Treatise onNavigation." Young Bouguer learnt mathematics of his fa ther, from the time he was able to speak, and thus became a proficient in those sciences while he was yet a child. He was sent very early to the Jesuit's college at Vannes, where he had the honour to instruct his regent in the mathematics, at eleven years of age. Two years after this he had a public contest with a pro fessor of mathematics, upon a proposi tion which the latter had advanced er roneously ; and lie triumphed over him ; upon which the professor, unable to bear the disgrace, left the country. Upon the death of his father, he was appointed to succeed in his office of hydrographer, af ter it public examination of his qualifica tions, being then only fifteen years of age ; an occupation which he discharged with great respect and dignity at that early age. In 1727, at the age of twenty nine, he obtained the prize proposed by the Academy of Sciences, for the best way of masting of ships. This first success of Bouguer was soon after followed by two others of the same kind ; he suc cessively gained the prizes of 1729 and 1731 ; the former for the best manner of observing at sea the height of the stars; and the latter, for the most advantageous way of observing the declination of the magnetic needle, or the variation of the compass.
In 1730, he was removed from the port of Croisci to that of Havre, which brought him into a nearer connection with the Academy of Sciences, in which he obtain ed, in 1731, the place of associate geome trician, vacant by the promotion of Mau pertuis to that of pensioner; and in 1735 he was promoted to the office of pension er astronomer. The same year he was sent on the commission to South America, along with Messieurs Godin, Condamine, and Jussieu, to determine the measure of the degrees of the meridian, and the fi gure of the earth. In this painful and troublesome business, of ten years dura tion, chiefly among the lofty Cordelier mountains, our author determined many other new circumstances, beside the main object of the voyage ; such as the expan sion and contraction of metals and other substances, by the sudden and alternate changes of heat and cold among those mountains; observations on the refrac tion of the atmosphere from the tops of the same, with the singular phenomenon of the sudden increase of the refraction, when the star can be observed below the line of the level ; the laws of the density of the air at different heights, from ob servations twade at different points of these enormous mountains; a determina tion that the mountains have an effect up on a plummet, though he did not assign the exact quantity of it ; a method of estimating the errors committed by navi gators in determining their route ; a new construction of the log for measuring a ship's way: with several other useful im provements.
Other inventions of Bouguer, made up on different occasions, were as follow : the heliometer, being a telescope with two object glasses, affording a good me thod of measuring the diameters of the larger planets with ease and exactness his researches on the figure in which twt, lines or two long ranges of parallel trees appear : his experiments on the famous reciprocation of the pendulum; andthose upon the manner of measuring the force of the light, &c. &c.
The close application which Bouguer gave to study undermined his health, and terminated his life the 15th of August, 1758, at 60 years of age. His chief works, that have been published, are,I. " The Fi gure of the Earth, determined by the Ob servations made in South America ;" 1749, in 4to. 2. " Treatise on Naviga tion and Pilotage ;" Paris, 1752, in 4to. This work has been abridged by M. La Caille, in one volume, 8vo. 1768. 3. " A Treatise on Ships, their Construction and Motions ;" in 4to. 1756. 4. " An Optical Treatise on the Gradation of Light;" first in 1729 ; then a new edition in 1760, in 4to. and a great number of papers insert ed in the Memoirs of the Academy.