(b. Bourg-en-Bresse, France, 9 October 1869: d. Sévres, France. 16 April 1951)
Cotton’s mother died when he was two years old. and he was raised by his father, Eugéne, a secondary school mathematics teacher, in comfortable rural surroundings. Following his father’s wishes, he prepared for a teaching career and in 1890 entered the École Normale Supérieure in Paris. The École Normale was then the chief cradle of French scientists, and Cotton made lifelong friendships with many future leaders, for example, Élie Cartan. In 1893 he passed the agrégation in physics and in 1895 became a teacher at a lycée in Toulouse. He received favorable reports from his superiors—’intelligent and hard-working,’ “upright and friendly,” “assiduously frequents the laboratory”—and in 1900 was recalled to the Ecole Normale to serve as suppléant to Jules Violle.
Cotton quickly became a member of the circle of the École Normale and other scientists that centered on Pierre Curie. Among them was Eugénie Feytis, a teacher and physicist, whom he married in 1913. Cotton was promoted in 1910 to adjoint professor and in 1920 moved to the Sorbonne as professor of theoretical physics and celestial physics; in 1922 he took the chair of general physics, Elected to the Academy of Sciences in 1923, he was its president in 1938. Usually modest and reserved, Cotton revealed a bold inner spirit on alpinist and hunting excursions, and became almost loquacious at congresses devoted to Esperanto, which he saw as an important means toward international understanding.
In his research Cotton, inspired particularly by Louis Pasteur and Curie, carried forward the French tradition of working toward the essential nature of matter through simple experiments illuminated by the plainest logic. This program used symmetries, notably those found in optical investigation, as the key to discovering the most characteristic properties of materials. Although it was a different approach, through spectroscopy, that would lead in the 1920’s to quantum mechanics, the classical path that Cotton followed eventually became no less important for the rise of condensed-matter physics.
In his doctoral dissertation, undertaken at the École Normale and defended in 1896, Cotton began with the familiar facts of birefringence and dichroism—the properties of certain crystals to refract and absorb light differently in different planes of polarization—and discovered a similar dichroism. in colored liquids, for opposite circular polarizations. He also discovered anomalous rotatory dispersion: the rotation of the plane of polarization showed a predictable variation with frequency in the neighborhood of a color absorption band.
In 1903 Cotton joined his École Normale classmate Henri Mouton in improving the new ultramicroscope, which could reveal submicroscopic objects as points of diffracted light. They used it for a wide variety of studies, taking a particular interest in colloids. Imposing a magnetic field on certain colloids, they found not only birefringence (previously seen by Ettore Majorana) but also circular dichroism: moreover, by freezing the tiny colloidal particles in gelatin, the pair proved that such optical effects were connected with the tendency of the anisotropic particles to line up with the magnetic field. Thenext step was to invisible molecules. Jean Perrin, another member of the Curie circle, was just then working up definitive proofs of the atomic theory of matter, which was still under a cloud in France: to connect optical properties with the orientation of molecules, seen as real physical entities, was less simple than it would later appear. In 1907 Cotton and Mouton closed the question by demonstrating magnetic birefringence in pure liquids such as nitrobenzene.
Meanwhile the discovery of the Zeeman effect in 1896 offered a hope that by altering spectral lines with magnetic fields, such effects as polarization could lead a researcher into the heart of atoms. Cotton had worked on the subject from the beginning: his most useful product was an instrument, later widely used, that could accurately measure magnetic fields by their influence on a current element in one arm of a balance. Further results came when he visited Zurich to collaborate with Pierre Weiss, a close friend and fellow École Normale graduate, who had built an electromagnet larger than any in France. Their 1907 measurement of the electron’s charge-to-mass ratio (e/m), using the Zeeman effect, was the best then available. Cotton began to campaign vigorously for a large magnetism laboratory for France, and in 1912 the University of Paris gave fifty thousand francs to begin work.
World War I interrupted the project. Cotton and Weiss collaborated to develop a system of locating enemy cannon by listening for the blasts with widely spaced microphones, and with the help of other physicists they installed teams at the front to guide counter-battery fire. This sound-ranging work was one of the chief contributions physics made to the military effort.
After the war fund-raising for the magnetism laboratory had to begin anew. With no little effort Cotton got support from the university and the gov ernment, from funds the Academy of Sciences raised through public subscription and bequests, and directly from industrialists. In 1928 he completed a giant electromagnet at Bellevue, outside Paris. Weighing more than one hundred tons, it generated seventy thousand gauss and required water cooling to handle its nearly one hundred kilowatts of power.
In its day the magnet was among the largest experimental devices in any country. It proved its worth in Solomon Rosenblum’s study of alpha rays, which revealed the fine structure of their differing velocities; in Louis LePrince-Ringuet’s studies of the “penetrating component” of cosmic rays, later known as mu-mesons; in Pierre Jacquinot’s Zeeman studies confirming and extending the nonlinear effects that Peter Kapitza had found in England; in the pioneering work of Franz (Francis) Simon and his collaborators, who obtained low temperatures by adiabatic demagnetization; and in many studies of the magnetic properties of condensed matter. As director of the Bellevue laboratory Cotton assigned research time at the magnet to physicists from numerous nations. He also built up auxiliary facilities such as a major spectroscope.
A firm believer in the French republic and an outspoken antifascist, Cotton was arrested along with several other professors in October 1941 and held for a month, probably to forestall any attempt at organizing an Armistice Day demonstration against the German occupation. He was arrested again for three days in April 1942 but otherwise worked unmolested at Bellevue through the war. He continued to be active into his late seventies, when failing health removed him from the laboratory life he loved.
I. Original Works. Cotton’s writings include Le phénomene de Zeeman (Paris, 1899); Les ultramicroscopes et les objets ultramicroscopiques (Paris, 1906), written with Henri Mouton: Lathéoric de Ritz du phénoméne de Zeeman (Paris, 1934): an extract from Le radium, journal de physique: La polarimétrie en lumiére ultraviolette (Paris, 1934): and Quelques instruments nouveaux de la section de physique du Palais de la découverte (Paris, 1943), a pamphlet. Many of Cotton’s writings are collected in Oeuvers scientifiques d’Aimé Cotton (Paris, 1956), which includes a bibliography. Some correspondence is held by the physics laboratory of the École Normale Supérieure. Paris. and bureaucratic particulars of Cotton’s career are in the Archives Nationales, Paris. F1724, 865.
II. Secondary Literature. Biographical works are Eugénie Cotton, Aimé Cotton (Paris, 1967); and Jean Rosmorduc. “Aimé Cotton: Le savant. l’homme. lecitoyen” (thése de 3me, cycle. University of Western Brittany, 1971).
Spencer R. Weart