(b. Paris, France, 14 September 1724; d. Paris, 8 March 1803)
Jeaurat’s maternal grandfather was the noted engraver Sébastien Leclerc. Because his father also pursued that art form and his uncle was a painter, it was appropriate that Jeaurat’s early years were spent in painting and engraving (he won a medal for drawing from the Academy of Painting), although he also studied mathematics under Lieutaud. His subsequent efforts in mapmaking, including work under Cassini de Thury, and in preparing a treatise aimed at rendering artistic perspective more rigorously geometric soon led him into scientific pursuits, a professorship in mathematics at the École Militaire in Paris, and astronomical studies.
The most important of his first works was concerned with perfecting planetary tables, especially those of Jupiter and Saturn, by comparing recorded oppositions with tabular predictions. In 1760 he pierced the roof of an attic at the École Militaire and began his own observations of those phenomena. He became a member of the Paris Academy of Sciences in 1763;and the results of these efforts were presented to that body, first as memoirs and then, in 1766, as completed tables of the motions of Jupiter.
Although a more permanent and better-equipped observatory was established at the École Militaire in 1769 under his direction, Jeaurat went to live at the royal observatory in 1770. Some of his subsequent work, such as his invention of a “double-image telescope, was devoted to the improvement of instruments. But far more important was his assumption of the editing of the Connaissance des temps.. The twelve volumes that he prepared, for the years 1776-1787, were enriched by a number of tables and catalogs: reimpressions, such as J. T. Mayer’s catalog of zodical stars in the volume for 1778 original efforts by others, such as Messier’s list of nebulae (1783); and his own contributions, such as his calculations of the principal towns, cities, and landmarks of France according to the operations forming the basis of Cassini’s map 1787.
Attainment of pensioner rank in 1784 led Jeaurat to abandon his work on the Connaissance des temps. Indeed, although he later served the Academy as vice-director (1791) and director (1792), his subsequent contributions consisted largely of protests that his work was being slighted or unjustly criticized.
Partly because of this record of jealousy but also because he had risen within the Academy as a geometer while pursuing almost solely astronomical work, Jeaurat was not among the original members of the First Class of the Institut de France and was not elected to its astronomical section until late in 1796. Neither this recognition nor his regaining of lot lodgings at the observatory, pitiably and unsuccessfully requested many times between 1793and1786, restored him to the status of contributing scientist.
I. Original Works. Since there exist several discrepancies in the list of Jeaurat’s works as recorded in such standard references as Poggendroff, Quéerard, and even the catalog of the Bibliothéque Nationale, only those works mentioned by Jeaurat himself in the Indication succincte des travaux scientifiques publiés áa Paris . . . Par le citoyen Edme-Séebastien Jeaurat . . . are indicated here. Nevertheless, minor problems remain, because late in his career he brought out at least three such Indications or Notices in support of various appeals-such as for a “national recompense and for membership in both the Institut National and the Bureau des Longitudes; these lesser questions, involving only his contributions to the Academy’s Méemories and not his separately published works, have been satisfactorily resolved.
Jeaurat’s first work was his Traitéde perspective á L’ usage des artistes . . . (Paris, 1750) . Prior to his election to the Academey, he presented several memoires there, four of which were printed in Mémoires de mathématique et de physique, préesentés á l’ Acadéemie royale des sciences . . ., 4 (1763:”Observations de la cométe de 1682, 1607 et 1531, faites en mai 1759, “pp.182-187;”Projection géométrique des éclipses de soleil, assujétie aux régles de la perspective ordinaire,”pp.318-335; “Méemoire sur le mouvement des planéetes, et moyen de calculer leur équation du centre pour un temps donné” pp. 554-540; and” Déetermination directe de la distance d’s une planéete au soleil de sa parallaxe et de son diaméetre horizontal pour un temps donné” pp. 601-611. His 1761 observation of the transit of Venus was published in the Academy’ regular Mémoires (1762), pp. 570-577, perhaps because the diagrams accompanying it were placed on the same plate as those bearing upon Lalande’s simultaneous observation
His presentations of the next several years were concerned primarily with oppositions of Saturn and, particularly, Jupiter, although those from 1769, 1772, and 1779 also included his observation, respectively, of the Venus transit and solar eclipse of 1769, of Venus in its greatest elongation in 1772, and a determination of the position of 64 stars of the Pleiades. See the Mémoires, as follows:(1763), 85-120, 241-215, 252-259;(1765), 376-388, 435-438 (1766), 100-119;(1767), 252-255, 266-267, 340-342 483-486;(1768), 91-92;(1769), 147-152;(1772), pt.2, 35-43;(1779), 505-525. The results of the earlier parts of these investigations were brought together in Essai sur la théorie des satellites de Jupiter, avec les tables de Jupiter (Pairs, 1766).
Although Jeaurat had occasionally dealt with eclipses and occultations prior to assuming the editing of Connaissance des temps—for instance, Mémoires (1766), 407-415, 417-422, it became a major subject of his contributions to the Mémoires thereafter:(1776), 268-272, 438-440;(1777) 487-490;(1778), 39-43;(1781), 9-20;(1785), 229-232;(1787), 5-6;(1788), 742-746. More important were his “instrumental” memoirs: one on experimentation with various types of glass and combinations of lenses for making achromatic objectives (1770), 461-486;two on his “double-image” telescope (1779), 23-50and (1786), 562-571; and one describing his astéréométre (1779), 502-504. An observation of Uranus in opposition (1787), 1-4;and a study of the nonapplication of the aberrational correction in the calculation of transits (1786), 572-573, complete his contributions to the Mémoires.
Virtually all of Jeaurat’s mathematical works and astronomical observations of the 1790’s remain in MS. One exception is a 1793 memoir, Méthode graphique de la trisection de l’angle, suivie de la relation des sinus, tangentes et secantes de10°de20°de40°de50°de70°, et de80°,”submitted to the Committee of Public Instruction; Jeaurat published an extract of this work, Relations Géométriques, at his own expense.
II. Secondary Literature. Although brief, the account of Jeaurat by J. M. Quérard in his La France littéraire ou Dictionnaire bibliographique des savants . . ., IV (Paris, 1830), 222-223, includes a complete listing of his articles in the Mémoires but, apparently erroneously, credit him with at least one nonexistent”“searatel publishe”work. Later short accounts, depending on Quéard, repeat that error while adding little of importance:J. F. Michaud, ed., Biographie universelle, XXI (Paris, 1858), 27-28 and Niles Nilesen, Géométres francais du dix-huitiéme siécle (Paris, 1935), pp.212-215. The best account of his astronomical work remains J. B. J. Delambre, Histoire de l’astronomie au dix-huitiéme siécle (paris, 1826), pp. 748-755. On his first observational locales, see G. Bigourdan,“Histoire des observatoires de l’École militaire,” in Bulletin astronomique, 4 (1887), 497-504, and 5 (1888), 30-40.
Seymour L. Chapin