(b. Beaugency, France, 12 November 1746; d. Paris, France, 7 April 1823),
Almost nothing is known of Charles’s family or of his upbringing, except that he received a liberal, nonscientific education. As a young man he came to Paris, where he was employed as a petty functionary in the bureau of finances. In a period of governmental austerity, Charles was discharged from this position, and owing to the pervasive influence of Franklin (who was visiting France in 1779), he set about learning the elements of nonmathematical, experimental physics. In 1781, after only eighteen months of study, Charles began giving a public course of lectures which, because of the eloquence of his discourse and the variety and precision of his experimental demonstrations, soon attracted a wide audience of notable patrons.
Charles was named a resident member of the Académie des Science on 20 November 1795. He was professor of experimental physics at the Conservatoire des Arts et Métiers, librarian of the Institute, and, from 1816, president of the Class of Experimental Physics at the Academy.
In 1804, Charles married Julie-Françoise Bouchard des Hérettes, an attractive young lady who achieved notoriety through her intimate friendship with the poet Lamartine. She died in 1817 after a long illness.
Charles was known to his contemporaries primarily through his contributions to the science of aerostation (ballooning). Shortly after the famous balloon experiments of the Montgolfier brothers, Charles conceived the idea of using hydrogen (“inflammable air”) instead of hot air as a medium of displacement. With the aid of a pair of clever Parisian artisans, the brothers Robert, Charles developed nearly all the essentials of modern balloon design. He invented the valve line (to enable the aeronaut to release gas at will for a descent), the appendix (an open tube through which expanded gas could freely escape, thus preventing rupture of the balloon sack), and the nacelle (a wicker basket suspended by a network of ropes covering the balloon and held in place by a wooden hoop). To prevent the subtle hydrogen gas from escaping through the balloon, Charles covered the taffeta sack with an impervious mixture of rubber dissolved in turpentine.
On 1 December 1783 Charles and the elder Robert ascended from Paris in their newly constructed Charlière (An unmanned trial balloon had been successfully launched in August.) The two aeronauts landed in a small village twenty-seven miles from Paris, and Charles continued the voyage on his own three miles farther. The king, who was at first opposed to this dangerous experiment, afterward granted Charles lodgings in the Louvre.
Charles published almost nothing of significance. The law which bears his name was discovered by him in about 1787, but it was first made public by Gay-Lussac (and at about the same time by Dalton). In his article on the expansion of gases by heat, Gay-Lussac described, criticized, and considerably improved upon Charles’s experimental procedure.
Apart from his experiments on gaseous expansion and his contributions to aerostation, Charles’s achievements in science were relatively minor. He is usually attributed with the invention of the megascope, a device to magnify large objects. He also made an improved hydrometer and invented a goniometer for measuring the angles of crystals.
Assertions to the contrary notwithstanding, there is no evidence that Charles knew anything but the rudiments of mathematics. Through an unfortunate confusion of names, biographers and bibliographers have completely confounded J.-A.-C. Charles with another contemporary known only as Charles le Géomètre. This obscure mathematician—whose first names, date, and place of birth are unknown—was elected associé géomètre of the Academy in 1785; most biographers of J.-A.-C. Charles have falsely asserted that he entered the Academy in this year. Charles le Géomètre was royal teacher of hydrodynamics, author of numerous articles on mathematical subjects, and one of the editors of the mathematical section of the Encyclopédie méthodique. Since Charles le Géomètre died in 1791, a year for which (because of the Revolution) the Academy published no memoirs, the usual éloge by the secrétaire perpétuel does not exist for him.
I. Original Works. Charles published no works of major significance. The articles that Poggendorff attributes to him—with the exception of one on electricity in the Journal de physique—were actually written by Charles le Géomètre.
II. Secondary Literature. An article on Charles appears in Charles Brainne, Les hommes illustres de l’Orléanais, 2 vols. (Orlcens, 1852); see also J,-J. Fourier, Éloge, in Mémories de l’Académie Royale des Sciences de l’Institut de France, 8 (1829), pp. lxxiii-lxxxvii; all the important facts concerning Charles and his wife as well as a few letters have been published by Anatole France in his L’Élvire de Lamartine, Notes sur M. & Mme. Charles (Paris, 1893).
For Charle’s experiments on gaseous expansion, see Annales de chimie, 43 (1802), 157 ff; on the distinction between J,-A,-C. Charles and Charles le Géomètre, we have only the information in Index biographique des members et correspondants de l’Académie des Sciences (Paris, 1954).
J. B. Gouch