MAIRAN, JEAN JACQUES D’ORTOUS DE

(b. Béziers, France, 26 November 1678; d. Paris, France, 20 February 1771)

physics.

Mairan was concerned with a wide variety of subjects, including heat, light, sound, motion, the shape of the earth, and the aurora. He wanted to find physical mechanisms (in the Cartesian sense) to explain phenomena. His theories were generally ingenious descriptions, which were sometimes mathematical and sometimes based on experiment. Despite his enthusiasm and diligence, Mairan often failed to perceive what was trivial and what was crucial about a theory or phenomenon. Nevertheless, Mairan was an important and sometimes controversial figure in the scientific community of his day. Working in the decades during which Newtonian ideas were becoming known in France, Mairan incorporated some of them in his theories; but he remained basically Cartesian.

Mairan’s family came from the minor nobility. His parents were François d’Ortous de Mairan and Magdaleine d’Ortous. After studying classics at Toulouse, Mairan studied physics and mathematics in Paris, where Malebranche was one of his teachers. On returning to Béziers in 1704, Mairan continued to be interested in science, and in the years 1715 to 1717 he published his first major works, which received prizes from the Bordeaux Academy. In 1718 Mairan went to Paris and became a member of the Academy of Sciences. (He was made an associate member right away, an unusual procedure.) He later received official lodging in the Louvre. Mairan was secretary of the Academy from 1741 to 1743, succeeding Fontenelle, and he was made pensionnaire géomètre in 1746. He also belonged to the Royal Societies of London, Edinburgh, and Uppsala, the Petersburg Academy, and the Institute of Bologna. Mairan was an amateur pianist, he had a serious interest in Chinese culture, and he attended the Paris salons.

Like most of his other work, Mairan’s work on heat continued over a long period and was ambitiously conceived. Mariran tried to explain temperature variations and changes of state. His theory of heat was essentially kinetic, but he felt that a subtle matter was necessary to account for the motions of the ultimate particles of ordinary matter and for the changes in these motions. On the basis of observations, experiments, and ingenious estimates, Mairan concluded that the earth has a “central fire” which is an important source of its heat.

Mairan tried to construct a theory of light which would be a Cartesian modification of Newton’s theory. In analogy with light, he attempted to understand sound in terms of particles rather than waves. This theory was inspired by the fact that one can distinguish different pitches even when they are all produced together. Mairan postulated different species of particles to carry the different pitches in the propagation of sound.

Marian’s most intense controversies were associated with his ideas in mechanics. He became involved in the notorious vis viva controversy, arguing that the “force of a body” depends on its velocity rather than the square of its velocity. Contrary to some, Mairan was aware that velocity should be treated as a vector quantity, but his arguments in general did not provide any special clarification of the problem.

In connection with the shape of the earth, another controversial topic, Marian tried to reconcile pendulum measurements (indicating that the force of gravity is weaker at the equator) with the Cassinis’s (erroneous) measurements of the length of a degree along the meridian (indicating that the earth is elongated at the poles). Mairan proposed that attraction at a point on the earth varies, not according to Newton’s law, but inversely as the product of the two principal radii of curvature!

BIBLIOGRAPHY

I. Original Works. Mairan’s works include Dissertation sur les variations du baromètre (Bordeaux, 1715); Dissertation sur la glace (Bordeaux, 1716; Paris, 1749); Dissertation sur la cause de la lumieère des phosphores et des noctiluques (Bordeaux, 1717); “Recherches géométriques sur la diminution des degrés terrestres en allant de L’s equateur vers les poles,” in Mémoires de l’Académie royale des sciences (1720); “Dissertation sur l’estimation et la mesure des forces motrices des corps,” ibid. (1728); “Discours sur la propagation du son dans les différens tons qui le modifient,” ibid. (1737).

More of Mairan’s works are listed in J. C. Poggendorff, Biogrpahisch-Literarisches Handwōrterbuch, II (Leipzig, 1863), 18, and in the study by Kleinbaum mentioned below.

II. Secondary Works. Abby R. Kleinbaum, Jean Jacques Dortous de Mairan (1678–1771): A Study of an Enlightenment Scientist (Columbia Univ. Ph. D. diss., 1970), is an excellent study of Mairan’s scientific work. The éloge of Mairan, by Grandjean de Fouchy, is in the Histoire de l’Académie royale des sciences, 1771 (Paris, 1774), 89–104. There is a discussion of Mairan’s work with respect to Newtonianism and Cartesianism in Pierre Brunet, L’introduction des theéories de Newton en France au XVIII Siècle (Paris, 1928); Mairan’s work on the shape of the earth is discucsed in I. Todhunter, A History of the Mathematical Theories of Attraction and the Figure of the Earth (New York, 1962), I, 59–61; Mairan’s role in the vis viva controversy is discussed in René Dugas, A History of Mechanics (Neuchâtel, 1955); Mairan’s work on the aurora is discussed in J. Morton Briggs, “Aurora and Enlightement,” in Isis., 58 (1967), 491–503.

Sigalia C. Dostrovsky