Fouchy, Jean-Paul Grandjean De

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Fouchy, Jean-Paul Grandjean De

(b. Paris, France, 10 March 1707; d. Paris, 15 April 1788)


He was the son of Marie-Madeleine Hynault and Philippe Grandjean de Fouchy, a Maconnais noble who perfected the printing of deluxe editions under Louis XIV. Trained to succeed his father, Fouchy (who called himself alternately Grandjean, Grandjean de Fouchy, and de Fouchy) made some contributions in that area but soon found his art less appreciated and the demand for such work diminished. He became auditor of the Chambre des Comptes and secretary to the duc d’Orleans. More important, he undertook the study of science, devoting himself particularly to astronomy as a student of Joseph Nicolas Delisle.

In 1726 he became part of the newly formed Society of Arts in Paris. Among the several papers he presented to this group was one on the meridian of mean time, an innovation destined to be his most lasting contribution to astronomy. Named to the Academy of Sciences as a supernumerary assistant astronomer in 1731, he succeeded to regular membership in astronomy by the end of 1733. The first decade of his membership therein was his most productive scientific period.

Many of the memoirs he offered during that period were simply observational reports of specific phenomena such as eclipses, occultations, and the 1736 transit of Mercury. A few were more general: in 1731, a proposal for giving astronomical tables a more commodious form; in 1732, a memoir dealing with the reason for the disappearance of Jupiter’s satellites from view before immersion and their reappearance only after a segment had emerged from Jupiter’s shadow, and establishing rules to calculate the size of the segments involved based upon a new observational technique; in 1733, a method of employing bright spots on the moon for longitude determination; in 1737, his observation of Mercury’s transit by a new means; in 1738, the proposal of a method to determine the eccentricity of the earth’s orbit and that of the inner planets; in 1740, the extension of this method to any planet; and finally, also in 1740, a suggestion for improving Hadley’s quadrant by substituting a telescope for open sights. Several other ideas for instrumental improvements, including a new level, a universal micrometer, and a device for moving a large quadrant, appeared in the collection Machines et inventions approuvées par l’Académie.

Unfortunately, these works were not as significant as they might seem. Few of them offered the advantages claimed by Fouchy, who, moreover, was much more prone to propose than to pursue. In the case of Jupiter’s satellites, for example, it remained for Jean Sylvain Bailly to develop his idea and arrive at important results. Thus, Delambre’s judgment that Fouchy was more an amateur than a true astronomer seems valid. This evaluation becomes even more appropriate after 1743, when Fouchy became the Academy’s perpetual secretary. He served alone in that capacity for thirty years; but from 1773 until he resigned in 1776, he asked for and received the aid of Condorcet. During that period he wrote over sixty éloges, which, although lacking the style and philosophy of those of Fontenelle and Condorcet, were noteworthy for their information on, and analysis of, the scientific work of others.

During his secretariat his scientific contributions consisted mainly of meteorological observations but also included observations of eclipses and of the transits of Venus of 1761 and 1769. Some of these activities he continued thereafter, for he remained active nearly to the end of his life, even dispassionately describing a strange malady that afflicted him in 1784. His long career brought him membership both in the Academy of Sciences of Berlin and the Royal Society of London.

Fouchy was married twice, to Mlle. de Boistis-sandeau and to Mlle. Desportes-Pardeillan. The first union produced one daughter; the second, one daughter and two sons, both of whom pursued military rather than scientific careers.


I. Original Works. The most important of Fouchy’s contributions to the Mémoires de l’Académie royale des sciences were “Sur la forme la plus avantageuse qu’on puisse donner aux tables astronomiques” (1731), 433–442; “Sur la féconde inégalité des satellites de Jupiter” (1732), 419–427; “Observation du passage de Mercure sur le disque du Soleil, arrivé le 11 novembre 1736” (1737), 248–252; “Méthode pour déterminer par observation, l’excentricité de la Terre, et celle des planètes inférieures” (1738), 185–192; “Second mémoire sur l’excentricité des planètes” (1740), 235–242; and “Mémoire concernant la description et l’usage d’un nouvel instrument pour observer en mer les hauteurs et les distances des astres” (1740), 468–482. His longitude determination proposal was recorded, under the heading of “Sur une nouvelle méthode pour les longitudes,” in the Histoire de l’Académie royale des sciences (1733), 76–79. His various instrument proposals may be read in Machines et inventions approuvées par l’Académie royale des sciences depuis son établissement jusqu’ à présent, avec leurs descriptions, 7 vols. (Paris, 1735–1777), V, 91–92; VI, 45–47, 79–81, 113–114; and VII, 47–48. His éloges appeared in his annual histories of the Academy’s work that preface the Mémoires. Those which appeared in the first sixteen years of his secretariat were also collected and published separately as Éloges des academiciens de l’Académie royale des sciences, morts depuis l’an 1744 (Paris, 1761).

II. Secondary Literature. The archives of the Académie des Sciences contain an interesting MS of notes by one of Fouchy’s sons for Condorcet’s use in preparing the official eloge. Condorcet’s product is in Oeuvres completes de Condorcet, Marie Louise Sophie de Grouchy, Marquise de Condorcet, ed., 21 vols. (Paris, an XIII [1804]), IV, 3–26. A far more valuable estimation of his work is in J. B. J. Delambre, Histoire de l’astronomie au dix-huitièrne siecle (Paris, 1826), pp. 327–331. For a very brief treatment, see Niels Nielsen, Geometres francais du dix-huitième siècle (Paris, 1935), pp. 184–185.

Seymour L. Chapin