Dufay (Du Fay), Charles-François Decisternai

(b. Paris, France, 14 September 1698; d. Paris, 16 July 1739)

physics.

Dufay came from a family that had followed military careers for over a century. He himself joined the Régiment de Picardie as a lieutenant in 1712, at the warlike age of fourteen; apparently he missed the closing battles of the War of the Spanish Succession, but he participated in the successful siege of Fuenterrabia (1718/1719), which helped force Philip V to abandon his adventures in Italy. Shortly after the campaign, Dufay accompanied his father and Cardinal de Rohan, the leading churchman in France, on an extended visit to Rome (1721). This marked the end of his military service. On his return to France in 1722 he became a candidate for the position of “adjunct chemist” in the Académie des Sciences, Paris.

This step did less violence to family tradition than might appear. Dufay’s grandfather, an amateur alchemist who appreciated the value of education, had sent his son, Dufay’s father, to the Jesuits at the Collège de Clermont. There he met the future cardinal and contracted a bibliomania that dominated his life after the loss of a leg ended his soldiering in 1695. Dufay grew up among his father’s books and erudite friends, “raised, like an ancient Roman, equally for arms and for letters” (Fontenelle). It was very likely Cardinal de Rohan who directed the attention of the scientific establishment toward the unknown young officer. The Academy’s leading scientist, Réaumur, and its titular head, the Abbé Bignon, managed Dufay’s candidacy, which terminated successfully in May 1723. He became associate chemist in 1724, pensionary in 1731, and director in 1733 and 1738.

Dufay very quickly justified the influence exercised in his favor. His first academic paper (1723), on the mercurial phosphorus, already displayed the characteristics which distinguished his later work: full command of earlier writings, clear prescriptions for producing the phenomena under study, general rules or regularities of their action, thorough study of possible complications or exceptions, and cautious mechanical explanations of a Cartesian flavor. This “phosphor”— the light sometimes visible in the Torricelli space when a barometer is jostled—much perplexed the physicists of the era, primarily because it did not always occur under apparently identical conditions. Dufay found that traces of air or water vapor occasioned the failures, which could be entirely eliminated with a technique of purification taught him by a German glassmaker. He explained the light in terms of Cartesian subtle matter squeezed from the agitated mercury; although he knew the work of Francis Hauksbee (the elder), he suggested no connection with electricity.

This maiden effort, however useful for the development of technique, did not provide a continuing line of research. For several years Dufay flitted from one subject to another: he studied the heat of slaked lime (1724), invented a fire pump (1725), touched on optics (1726), plane geometry (1727), the solubility of glass (1727), and the coloring of artificial gems (1728). He eventually published at least one paper in each of the branches of science recognized by the Academy, the only man, perhaps, who has ever done so. In 1728 he took up magnetism, the first subject to enlist his interest for an extended period. In the first of three memoirs he attacked the vexed question of natural magnetism: Under what conditions, and in what positions, do iron tools acquire a magnetic virtue? The apparent answer—oriented vertically—suggested an easy Cartesian model, for the “hairs” which determine the direction in which the magnetic effluvia pass through the pores of iron might be expected to line up under their gravity when the bodies containing them stand upright. The last two memoirs (1730, 1731), which attempt to measure the force of magnetic poles, are most instructive. Although Dufay took the greatest pains over the experiments, varying sizes, shapes, and measuring devices, he failed to find any simple relation between force and distance; the apparently straightforward procedures of Coulomb in fact are far from obvious.

In 1730 Dufay returned to his original subject, phosphorescence, with a memoir of great importance in the development of his method. Chemists had long been acquainted with a few minerals which, like the Bologna stone (BaS) and Balduin’s hermetic phosphor (CaS), glowed after exposure to light. Great mystery surrounded these expensive and supposedly rare substances. Dufay detested mysteries and held as a guiding principle that a given physical property, however bizarre, must be assumed characteristic of a large class of bodies, not of isolated species. He set about calcining precious stones, egg and oyster shells, animal bones, etc., most of which became phosphorescent; indeed, he found that almost everything except metals and very hard gems could be made to shine like Bologna stones. He gave clear recipes for producing the phosphors and patiently examined the endless variations in their colors and intensities: “How differently bodies behave which seemed so similar, and how many varieties there are in effects which seemed identical!” This line of work ended in 1735, with a study of the luminescence of gems. Dufay distinguished excitation by friction, by heat, and by light, and tried to find some general rules of their operation; but the phenomena proved altogether too complex, and he established little more than that diamonds usually can be excited in more ways than lesser stones.

In 1732 Dufay at last found a subject ripe for his practiced talents. A year earlier Stephen Gray had published an account of his discovery that “electricity”—the attractive and repulsive “virtue” of rubbed glass, resins, precious stones, etc.—could be communicated to bodies, like metals or human flesh, which could not be electrified by friction. Gray had also succeeded in transmitting the virtue of a glass tube through lengths of stout cord suspended by silk threads. It appeared to Dufay that electricity, far from being the parochial, effete effect discussed by earlier writers, was one of nature’s favorite phenomena. He proceeded as with the phosphors: first a survey of the existing literature, which became his initial memoir on electricity; next, an attempt to electrify every natural object accessible to experiment. As he expected, all substances properly treated—save metals, animals, and liquids—could be electrified by friction; while all bodies whatsoever could be made so by communication. In the process he distinguished insulators from conductors more sharply than Gray had done and ended the desultory search for new electrics which had characterized the study of electricity since the time of Gilbert.

Dufay’s most notable discoveries (1733) resulted from an attempt to clarify the connection between electrostatic attraction and repulsion. Ever since Hauksbee had found that light objects drawn to a glass tube are sometimes forcibly driven from it, physicists had tried to understand the relation between motions toward and away from an excited electric. Hauksbee had given incompatible theories; others, like the Dutch Newtonian W. J. ’sGravesande, taught that the tube possessed an electrical “atmosphere” whose pulsations caused alternate “attractions” and “repulsions,” an elegant theory which, however, misrepresents the facts; and still others suspected, as Dufay did initially, that repulsion did not exist at all, an object apparently repelled by an excited electric in fact being drawn away by neighboring bodies electrified by communication. Further experiment suggested another possibility to him: Since substances the least excitable by friction, like the metals, respond most vigorously to the pull of the tube, might not “an electric body attract all those that are not so, and repel all those that become electric by its approach, and by the communication of its virtue?” The apparent confirmation of this capital insight—bits of metal electrified by the tube were found to repel one another—may be regarded as the decisive step in the recognition of electrostatic repulsion, the uncovering of the phenomenological connection between motions toward and away from the tube. It also prepared the way for a detection still more surprising.

Experience had taught Dufay not to draw general conclusions without examining a wide range of substances. Accordingly he tried electrifying one of the two metal bits by a rod of gum copal; the resultant attraction, which flabbergasted him, soon forced him to recognize the existence of two distinct “electricities,” and to determine their basic rule of operation. This “bizarrie” (as Dufay called the double electricities) proved a great difficulty for the usual theories of electricity, which relied solely on matter in motion. Dufay expected that a representation in terms of vortices might someday be found, but he did not insist; he was concerned first to establish the regularities and only later to add the mechanical pictures. In this point of method Benjamin Franklin— and not Dufay’s protégé the Abbé Nollet—was his lineal descendant.

From his classic researches on the two electricities Dufay turned to Gray’s quixotic experiment of the charity boy, the electrification of a small insulated orphan. Playing the leading part himself, Dufay received a sharp shock when an assistant tried to touch him, the stroke penetrating even his waistcoat and shirt; and both he and Nollet noticed that a spark passed just before contact when the experiment was repeated at night. These phenomena utterly astounded him, inured though he was to “meeting the marvelous at every turn.” He devoted great effort to studying the electric light, to which his earlier research on phosphors naturally inclined him. Here again he was stopped by the vast complexity of the phenomena, which gave no intelligible clue to the advancement of electrical theory.

Dufay’s substantial electrical discoveries—the relation between attraction and repulsion, the two electricities, shocks, and sparking—are but one aspect, and perhaps not the most significant, of his achievement. His insistence on the importance of the subject, on the universal character of electricity, on the necessity of organizing, digesting, and regularizing the known facts before grasping for more, all this helped to introduce order and professional standards into the study of electricity at precisely the moment when the accumulation of data began to require them. He found the subject a hodgepodge of often capricious, disconnected phenomena; he reduced the apparent caprice to rule; and he left electricity in a state where, for the first time, it invited prolonged scrutiny from serious physicists.

Electricity by no means exhausted Dufay’s energy or talent; between his sixth and seventh memoirs on the subject, he published papers on parhelia (1735), on fluid mechanics (1736), on dew (1736), on sensitive plants (1736), and on dyestuffs (1737). The last two studies were by-products of still another side of Dufay’s ceaseless activity. That on dyestuffs related to an onerous charge he had received from the government, namely the revision of standards for the closely regulated dye industry. The botanical paper grew out of an even larger job, the administration of the Jardin Royal des Plantes.

The Jardin, founded in 1635 as a medical garden and a school of pharmacy and medicine, had extended its functions under the inspired direction of the royal physician, Guy Crescent Fagon, who encouraged the study of chemistry and the expansion of the botanical collections. Regrettably Fagon’s successor, Pierre Chirac, a much more limited doctor who cared only for his own profession, neglected the garden and alienated the professors. A nonmedical man was needed to repair the damage. Dufay’s industry, wide interests, and practical good sense, not to mention his ministerial connections, made him an ideal administrator. With the advice of his friends the brothers Jussieu, who held chairs at the Jardin, Dufay replanted, built new greenhouses for foreign flora, and established close relations, including exchanges of specimens, with the directors of similar institutions elsewhere in Europe. His official visits to Holland and England (1733/1734), accompanied by Bernard de Jussieu and Nollet, advanced not only French botany, but— through connections formed by Nollet—French experimental physics as well. In the seven years of his intendancy Dufay transformed Chirac’s collection of weeds into “the most beautiful garden in Europe” (Fontenelle), providing the basis for the great expansion effected by his successor, the comte de Buffon.

Dufay’s diverse activities made him a careful economist of his time. Although his position, acquaintance, and good humor opened endless opportunities for social engagements, he preferred to live quietly, finding relaxation in the satires of Swift, in the small circle of his mother’s friends, or at the home of a kindred soul like the marquise du Châtelet. He never married It was a great blow to French science (and a measure of its incompetence) when, at the age of forty, Dufay succumbed to the smallpox.

BIBLIOGRAPHY

Dufay’s chief papers were published in the Mémoires de l’Académie des sciences (Paris). Among the most important are “Mémoire sur les baromètres lumineux” (1723), 295– 306; “Observations sur quelques expériences de l’aimant” (1728), 355–369; “Suite des observations sur l’aimant” (1730), 142–157; “Mémoire sur un grand nombre de phosphores nouveaux” (1730), 524–535; “Troisième mémoire sur l’aimant” (1731), 417–432; “Mémoires sur l’électricité” (1733), 23–35, 73–84, 233–254, 457–476; (1734), 341–36 503–526; (1737), 86–100, 307–325; and “Recherches sur la lumière des diamants et de plusieurs autres matières” (1735), 347–372. Dufay summarized his first electrical memoirs in “A Letter... Concerning Electricity,” in Philosophical Transactions of the Royal Society, 38 (1733/1734 258–266.

A full bibliography of the French papers is given in Nouvelle table des articles contenus dons les volumes de l’Académie royale des sciences de Paris depuis 1666 jusqu’en 1770 (Paris, 1775/1776), and in P. Brunet, “L’oeuvre scientifique de Charles-François Du Fay (1698–1739),” in Petrus nonius, 3 , no. 2 (1940), 1–19. Poggendorff omits several items published after 1735. I. B. Cohen, Franklin and Newton (Philadelphia, 1956), p. 616, gives complete titles of the memoirs on electricity. Dufay autographs are quite rare. There are a few unimportant letters among the Sloane Manuscripts at the British Museum; a dossier including notes of Hauksbee’s work and correspondence with Gray’s collaborator, Granville Wheler, at the Institut de France; several letters to Réaumur published in La correspondance historique et archéologique, 5 (1898), 306–309; and a few administrative documents noticed in A.-M. Bidal, “Inventaire des archives du Muséum national d’histoire naturelle,” in Archives du Muséum, 11 (1934), 175–230.

The biographical sources are surprisingly meager. The most important is Fontenelle’s “Éloge de M. Du Fay,” in Histoire de l’Académie des sciences (1739), 73–83; scattered data appear in G. Martin, Bibliotheca fayana (Paris, 1725); Les lettres da la marquise du Châtelet, T. Besterman, ed. (Geneva, 1958); Correspondence of Voltaire, T. Besterman, ed. (Geneva, 1953–1965); and J. Torlais, Un esprit encyclopédique en dehors de l’Encyclopédie. Réaumur, 2nd ed. (Paris, 1961).

For assessments of Dufay’s scientific work see the publications of Brunet and Cohen cited above; H. Becquerel, “Notice sur Charles François de Cisternai du Fay...,” in Centenaire de la fondation du Muséum d’histoire naturelle (Parts, 1893), pp. 163–185; J. Daujat. Origines et formation de la théorie des phénomènes électriques et magnétiques (Paris, 1945); and E. N. Harvey, A History of Luminescence (Philadelphia, 1957). For Dufay’s administrative accomplishments see A.-L. de Jussieu, “Quatrième notice historique sur le Muséum d’histoire naturelle,” in Annales du Muséum, 4 (1804), 1–19; and the bibliography in Y. Laissus, “Le Jardin du Roi,” in R. Taton, ed., Enseignement et diffusion des sciences en France au XVIIIe siècle (Paris, 1964), pp. 287–341.

John L. Heilbron