BOUGUER (Peter), an eminent mathematician and mechanical philosopher, was born at Croisic, in Lower Bretagne, on the 10th of February 1698. His father John Bouguer, who was likewise a considerable mathe-
matician, was then professor royal of hydrography at that port; and under him young Bouguer studied mathematics, and the application of them to ship-building, almost from the period when he began to speak; so that he was a proficient in these sciences before he had reached beyond the years of childhood. He was, however, removed from Croisic to the Jesuits college at Vannes, where, at 13 years of age, he triumphed, in a public contest, over a professor of mathematics, who had advanced a mathematical proposition erroneously. Two years after this he lost his father, whom he was appointed to succeed in the office of hydrographer, after being publicly examined, and giving the most complete proof of his being duly qualified to fill the vacant chair. He was indeed qualified by prudence as well as by science; for however surprising it may be, he filled it both with dignity and with abilities, though then not more than 15 years of age.
In the years 1727, 1729, and 1731, he gained the prizes successively proposed by the Academy of Sciences for essays on the best way of equipping ships with masts, on the best method of observing at sea the height of the stars, and on the most advantageous way of observing the declination of the magnetic needle or the variation of the compass. In 1729 he published an Optical Essay upon the Gradation of Light, in which he examined the intensity of light, and determined its degrees of diminution in passing through different pellucid mediums, and particularly in traversing the earth's atmosphere. Of this essay, which was written upon a subject that till then had not attracted the attention of philosophers, the reader will find some account in the Encyclopaedia Britannica, under the title Optics, no 32, &c.
In 1730 Bouguer was removed from the port of Croisic to that of Havre. In 1731 he obtained, in the Academy of Sciences, the place of associate geometer, vacant by the promotion of Maupertuis to that of pensioner; and in 1735 he was promoted to the office of pensioner-altronomer. The same year he was sent on the commission to South America, along with Messrs Godin, Condamine, and Jeuffieu, to determine the measure of the degrees of the meridian, and the figure of the earth. In this painful and troublesome business of ten years duration, chiefly among the lofty Cordelier mountains, our author, besides attending to the object of the voyage, made many scientific observations, viz. on the effect of the Cordeliers on the polarity of the magnetic needle; on the expansion and contraction of metals and other substances, by the sudden and alternate changes of heat and cold among those mountains; and on the refraction 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. He likewise ascertained the laws of the density of the air at different heights, from observations made at different points of those enormous mountains; he discovered that the mountains have an effect upon a plummet, though he did not assign the quantity of that effect; he found out a method of estimating the errors committed by navigators in determining their route; gave a new construction of the log for measuring a ship's way; and made several other useful improvements. M. Bouguer made at different times some important experiments on the famous reciprocation of the pendulum; he invented in 1747 the RELIO-