VERDET, MARCEL ÉMILE

(b. Nîmes, France 13 March 1824; d. Nîmes, 3 June 1866)

Physics.

Verdet was one of the outstanding physics teachers of mid-nineteenth-century France, holding professorships at the École normale supérieure. the École polytechnique, and the Faculté des sciences in Paris. He introduced into the French scientific world the thermodynamics of Joule, Clausius, Helmholtz, and William Thomson, and conducted important experiments on the effects of a magnetic field on plane-polarized light.

Little is known of Verdet’s background except that he came from a leading Protestant family in the south of France. An early preference for teaching led him to attend the École normale supérieure, rather than the École polytechnique, to which he was also accepted. At the close of his studies he scored so high on the concours d’ agrégation that he was spared the customary tour of duty in the provinces and appointed directly to the Lycée Henri IV in Paris. In 1848 he received his doctorat from the Sorbonne and was appointed lecturer in physics at the École normale, a position he held for the rest of his life. Four years later he became entrance examiner at the École polytechnique; then examiner in physics (1853) and professor of physics (1862). Later his fame as a teacher gained him the chair of mathematical physics at the Paris Faculté des sciences.

Verdet educated his colleagues as well as his students. French physicists of his time were ignorant of much of the research going on outside their country, so Verdet undertook to publish abstracts of the most important articles appearing in foreign journals. From 1852 to 1864 every volume of the Annales de chimie contained ten or more of his synopses. Since much of the work being done in England and Germany in this era centered on the development of the mechanical theory of heat, Verdet soon became the French expert in this subject. In 1864–1865 he taught the new thermodynamics at the Sorbonne, and the notes from his course were compiled by two students and published as La théorie mécanique de la chaleur, a textbook which has become a classic.

Verdet’s original scientific papers, although limited in quantity by his extensive academic duties, his short life, and poor vision, reveal a talent not as an innovator but, rather, as a painstaking investigator who filled in the details of others’ discoveries. His early research included a series of experiments on electromagnetic induction and a theoretical treatise on the image-forming power of lenses. In his major effort Verdet investigated the phenomenon now known as the “Faraday effect": the rotation of the plane of polarization of a ray of light by a transparent solid or liquid in a magnetic field (this effect was discovered by Michael Faraday in 1845). Verdet studied the dependence of the Faraday effect on the strength of the magnet causing the rotation, the medium in which the light is traveling, and the color of the light. He found that the magnetic power of rotation was directly proportional to the strength of the magnet, inversely proportional to the square of the wavelength of the light, and related to the index of refraction of the material. In recognition of the importance of this work a measure of the power of magnetic rotation was named “Verdet’s constant."

BIBLIOGRAPHY

I. Original Works. Verdet’s entire scientific output is collected in Oeuvres de Verdet, 8 vols. (Paris, 1868–1872), which includes all his scientific papers and the lectures notes from his courses. His writings include “Mémoires sur la physique publiés à l’étranger, extraits par M. E. Verdet” in Annales de chimie, 3rd ser., 34–69 , and 4th ser., 1–4 (1852–1864); La théorie mécnaique de la chaleur (Paris, 1868): “Recherches sur les phénomènes d’induction porduits par les décharges électriques,” in Annales de chimie, 3rd ser., 24 (1848), 377–405; “Note sur les courants induits d’orders supérieurs,” ibid., 29 (1850), 501–506; “Recherches sur les phénoménes d’induction porduits par le mouvement des métaux ...,” ibid., 31 (1851), 187–217; “Sur l’intensitédes images lumineuses formées au foyer des lentilles et des miroirs,” ibid., 489–503; and “Recherches sur les propriétés optiques développées dans les corps transparents par l’action du magnétisme,” ibid., 41 (1854), 370–412; 43 (1855), 37–44; 52 (1858), 129–168; and 69 (1863), 415–491.

II. Secondary Literature. The two best biographies of Verdet are by M. A. Levistal, in Annales scienctifiques de l’École normale supérieure, 3 (1866), 243–351; and A. de La Rive, in Mémorial de l’Association des anciens élèves de l’École normale 1846–1876 (Pairs, 1877).

Eugene Frankel