BOUGUER (Peter)
, a celebrated French mathematician, was born at Croisic, in Lower Bretagne, the 10th of February 1698. He was the son of John Bouguer, Professor Royal of Hydrography, a tolerably good mathematician, and author of A complete Treatise on Navigation. Young Bouguer was accustomed to learn mathematics from his father, 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 Jesuits' 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 professor of mathematics, upon a proposition which the latter had advanced erroneously; and he triumphed over him; upon which the professor, unable to bear the disgrace, left the country.
Two years after this, when young Bouguer had not yet finished his studies, he lost his father; whom he was appointed to succeed in his office of hydrographer, after a public examination of his qualifications; being then only 15 years of age; an occupation which he discharged with great respect and dignity at that early age.
In 1727, at the age of 29, 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 successively 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 1729, he gave an Optical Essay upon the Gradation of Light; a subject quite new, in which he examined the intensity of light, and determined its degrees of diminution in passing through different pellucid mediums, and particularly that of the sun in traversing the earth's atmosphere. Mairan gave an extract of this first essay in the Journal des Savans, in 1730.
In this same year, 1730, he was removed from the port of Croisic to that of Havre, which brought him into a nearer connection with the Academy of Sciences, in which he obtained, in 1731, the place of associate geometrician, vacant by the promotion of Maupertuis to that of pensioner; and in 1735 he was promoted to the office of pensioner-astronomer. The same year he was sent on the commission to South America, along with Messieurs Godin, Condamine, and Jeussieu, to determine the measure of the degrees of the meridian, and the figure of the earth. In this painful and troublesome business, of 10 years duration, chiefly among the lofty Cordelier mountains, our author determined many other new circumstances, beside the main object of the voyage; such as the expansion and contraction of metals and other substances, by the sudden and alternate changes of heat and cold among those mountains; observations 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; the laws of the density of the air at different heights, from observations made at different points of these enormous mountains; a determination that the mountains have an effect upon a plummet, though he did not assign the exact quantity of it; a method of estimating the errors committed by navigators in determining their route; a new construction of the log for measuring a ship's way; with several other useful improvements.
Other inventions of Bouguer, made upon different occasions, were as follow: The heliometer, being a telescope with two object glasses, affording a good method of measuring the diameters of the larger planets with ease and exactness: his researches on the figure in which two lines or two long ranges of parallel trees appear: his experiments on the famous reciprocation of the pendulum: and those 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,
1. The Figure of the Earth, determined by the observations made in South America; 1749, in 4to.
2. Treatise on Navigation and Pilotage; Paris, 1752, in 4to. This work has been abridged by M. La Caille, in 1 volume, 8vo, 1768.
3. Treatise on Ships, their Construction and Motions; in 4to, 1756.
4. Optical Treatise on the Gradation of Light; first in 1729; then a new edition in 1760, in 4to.
His papers that were inserted in the Memoirs of the Academy, are very numerous and important: as, in the Memoirs for 1726, Comparison of the force of the solar and lunar light with that of candles.—1731, Observations on the curvilinear motion of bodies in mediums.—1732, Upon the new curves called the lines of pursuit.—1733, To determine the species of conoid, to be constructed upon a given base which is exposed to the shock of a fluid, so that the impulse may be the least possible.—Determination of the orbit of comets.—1734, Comparison of the two laws which the earth and the other planets must observe in the figure which gravity causes them to take.—On the curve lines proper to form the arches in domes.—1735, Observations on the equinoxes.—On the length of the pendulum.—1736, On the length of the pendulum in the torrid zone.—On the manner of determining the figure of the earth by the measure of the degrees of latitude and longitude.—1739, On the astronomical refractions in the torrid zone.—Observations on the lunar eclipse, of the 8th of September 1737, made at Quito. —1744, Short account of the voyage to Peru, by the members of the Royal Academy of Sciences, to measure the degrees of the meridian near the equator, and from thence to determine the figure of the earth. —1745, Experiments made at Quito and divers other places in the torrid zone, on the expansion and contraction of metals by heat and cold.—On the problem of the masting of ships.—1746, Treatise on ships, their structure and motions.—On the impulse of fluids upon the fore parts of pyramidoids having their base a trapezium.—Continuation of the short account given in 1744, of the voyage to Peru for measuring the earth.—1747, On a new construction of the log, and other instruments for measuring the run of a ship.— 1748, Of the diameters of the larger planets. The new instrument called a heliometer, proper for determining them; with observations of the sun.—Observation of the eclipse of the moon the 8th of August 1748.—1749, Second memoir on astronomical refractions, observed in the torrid zone, with remarks on the manner of constructing the tables of them.— | Figure of the earth determined by MM. Bouguer and Condamine, with an abridgment of the expedition to Peru.—1750, Observation of the lunar eclipse of the 13th of December 1750.—1751, On the form of bodies most proper to turn about themselves, when they are pushed by one of their extremities, or any other point.—On the moon's parallax, with the estimation of the changes caused in the parallaxes by the figure of the earth.—Observation of the lunar eclipse, the 2d of December 1751.—1752, On the operations made by seamen, called Corrections.—1753, Observation of the passage of Mercury over the sun, the 6th of May 1753.—On the dilatations of the air in the atmosphere.—New treatise of navigation, containing the theory and practice of pilotage, or working of ships.—1754, Operations, &c, for distinguishing, among the different determinations of the degree of the meridian near Paris, that which ought to be preferred.—On the direction which the string of a plummet takes.—Solution of the chief problems in the working of ships.—1755, On the apparent magnitude of objects.—Second memoir on the chief problems in the working of ships.—1757, Account of the treatise on the working of ships.—On the means of measuring the light.—1758, His Eulogy.
In the volumes of the prizes given by the academy, are the following pieces by Bouguer:
In vol. 1, on the masting of ships.—Vol. 2, On the method of exactly observing at sea the height of the stars; and the variation of the compass. Also on the cause of the inclination of the planets' orbits.
