(b. Paris, France, 4 September 1711; d. Paris, 1 May 1796)
There seem to be few details of Pingré’s early life, but he is said to have been a somewhat precocious child with a great desire for knowledge. He was educated by the Congregation of Ste. Genevieve and in 1727, at the age of sixteen, entered the religious order of Ste. Genevieve de Senlis. There is no doubt of his intellectual abilities, for in 1735, when he was only twenty-four, he became professor of theology at the University of Ste. Genevieve. Like many French Roman Catholic clerics, Pingre followed the rather independent Augustinian opinions of the seventeenth-century bishop Cornelis Jansen; and when action was taken against the Jansenists in 1745, he was deprived of his chair and sent by his order to teach Latin in the schools outside Paris. Accused more than once of corrupting the minds of his young pupils, he was obliged to move from one place to another until the eminent surgeon Claude Le Cat decided to help him. In 1744 Le Cat had founded an academy of sciences in Rouen; and since the academy was still without an astronomer in 1749, he invited Pingre, who had recently moved to that city, to accept the post. It proved to be the turning point of Pingré’s career. He was later recalled to Paris, where he settled permanently as an astronomer but with literature, history, music and, in later life, botany as his hobbies. Contemporaries spoke of him with affection, and he seems to have been a pious, kindly, and tolerant man.
Pingré was thirty-eight when he began a serious study of astronomy, but within a year he was able to calculate the lunar eclipse of 23 December 1749 well enough for his results to be submitted to the Academie des Sciences in Paris. Certain writers of Pingré’s obituary notices state that through these calculations he found an error in the figures for the eclipse that Lacaille had prepared; but the evidence for this, and for the strong friendship between the two men, appears doubtful. Pingré’s rapidly growing abilities as an astronomer need not be questioned, however; and after he had made observations at Rouen of the transit of Mercury across the sun’s disk in 1753, his reputation was sufficient for the Academy to elect him a correspondant. Soon afterward his order recalled him to Paris and established a small observatory for him on the roof of the Abbey of Ste. Geneviève.
Also during 1753 Pingré began working with P. C. Le Monnier, who greatly encouraged him and whom he helped prepare État du ciel à l’usage de la marine, a nautical almanac giving hour angles of the moon for the purpose of determining longitude at sea by use of a method devised by Le Monnier. Although the work, which was complementary to the Connaissance des temps, did not find favor with mariners and appeared only for the years 1754 to 1757, it greatly enhanced Pingré’s reputation as a computer.
Indeed, Pingré was becoming well-known as an astronomer; and in 1755 he was appointed a member of the commission established that year to examine the measurement of an arc of the meridian made some eighty years before by Jean Picard. In 1756 the Academy honored Pingre by electing him associe libre, the highest rank of membership open to a cleric. Also about this time he was invited by the provost of the Paris guilds to design a sundial for the corn market that would display the entry of the sun into the various zodiacal signs; this involved Pingré in an observing program as well as much computation, and he did not complete the commission until 1764.
Under the leadership of Delisle, the French took a great interest in the transit of Venus that was to occur in 1761, and Pingre became involved in the international arrangements made to ensure that observations of a phenomenon allowing the sun’s distance to be precisely determined were carried out from points as widely scattered as possible. Commissioned by the Academy to observe from Rodriguez Island in the Indian Ocean, he left France early in January 1761.
This was during the Seven Years War; and since British naval supremacy might possibly present difficulties, Pingré armed himself with instructions from the British authorities commanding that he be unmolested and allowed to proceed without delay. His outward journey was uneventful until his ship met a damaged French vessel, the commander of which ordered Pingré’s ship to stay with him. Only Pingré’s dogged persistence got him and his assistant Denis Thuillier transshipped at last, and they arrived at Rodriguez with little time left to establish their observatory. At the transit on 6 June there was rain and cloud for a great part of the time, so that only a few observations could be made. The island was later sacked three times by the British; and the expedition’s ship was attacked and boarded on the way home, despite Pingré’s British instructions. Therefore, when the vessel reached Lisbon, Pingre decided to journey overland, reaching Paris late in May 1762. The expedition was not unsuccessful, for besides a few useful transit observations, Pingre had many longitude determinations, some of which led to a replotting of the Cape Verde Islands. His analysis of the observations led him to the rather large value of 10.6 seconds of arc for the solar parallax, a figure that he later modified.
On his return Pingre also became engaged in preparing a second edition of Lacaille’s L’art de verifier les dates, originally designed to give sufficient details of eclipses during the previous 1,800 years to serve as a guide for dating historical events. He checked all the calculations and added additional eclipses up to A.D. 1900. The new edition appeared in 1770; but Pingre continued to work on the subject, computing eclipses back to 1000 B.C. and publishing the results in the Mémoires de mathematique et physique... of the French Academy. He also took a leading part in the preparations for observing the 1769 transit of Venus, and in 1766 and 1767 he presented two reports to the Academy about suitable obaerving stations. Undaunted by his previous experiences—the war was now over—Pingre set forth on voyages in 1767, 1768 and 1771. They were primarily intended to check chronometers by Fersinand Berthoud and Leroy, but on the 1768 voyage he visited Haiti, where he observed the 1769 transit. Later he recomputed the solar parallax from the complete observations; and in 1772 he announced a value of 8.8 seconds of arc, a figure extremely close to the present figure of 8.794.
Having become astronomer-geographer to the navy, Pingre in 1769 was appointed chancellor of his old university. In 1772 he became librarian at Ste. Genevieve; and although in his sixties, he continued with his computing and began to take an increasing interest in old observations. Pingre put his immense classical knowledge to use in translating and editing the Astronomica of Marcus Manilius and the earlier Phaenomena of Aratus of Soli, and especially in preparing his most important work, the two-volume Cometographie ou traite historique et theorique des cometes (1783℃1784). This monumental work was divided into four parts, the first of which was a history of astronomy from Babylonian and Egyptian times, with particular reference to ideas about comets. The second part was a catalog of all comets observed since antiquity, with the orbital elements of 166 for which paths had been computed, 50 of them by Pingre himself. The third section discussed cometary returns, theories about the nature of comets, and the physical effects likely to ensue from their close approach to the earth. The fourth part concerned cometary orbits and methods for computing them. The high reputation of the Cométographie was deserved, and as recently as 1950 it was officially recommended as a source book of cometary information.
Pingré’s other great book, the purely historical Annales celestes du dix-septieme siecle, took him thirty years to complete and contained carefully checked and edited astronomical observations from the seventeenth century, both published and unpublished. In 1791 Le Monnier and Lalande persuaded the Academy to vote a large sum for its publication; but the printer was slow, and Pingré’s death in 1796, coupled with devaluation the preceding year, led the printer to abandon the project and to sell the printed sheets as wastepaper. Worse still, the manuscript was lost. Almost a century later, however, a Parisian bibliophile found in a country town what turned out to be Le Monnier’s set of sheets; and the remainder of the manuscript was discovered in the archives of the Paris observatory. In 1898, at the instigation of C. G. Bigourdain, the Academy again decided to publish; and the volume appeared in 1901. There is still a voluminous collection of Pingré’s unedited manuscripts at the library of Ste. Genevieve. They do not seem to be astronomical, however, but to cover his other interests, ranging from translations of Spanish voyages, history and historical criticism, and literary sketches to liturgical hymns, musical satires, and a vast amount of French and Latin poetry. It is as an astronomer, however, that Pingre is remembered.
I. Original Works. Pingré’s main works were Cometographie ou traite historique des cometes, 2 vols. (Paris, 1783℃1784); and Annales celestes du dix septieme siecle, C. G. Bigourdain, ed. (Paris, 1901).
II. Secondary Literature. The most complete biographical note is G. Riche de prony,“NOte sur la vie et les ourvages d’ Alexandre Gui Pingre,” in Memories de l’ Institut national des sciences et arts. Sciences mathematiques et physiques (an VI , 1 xxvi xlvi. There is also a reasonably full note on his astronomy,with some strictures on his accuracuy as an observer, by J. B. Delambre (Paris, 1827), 664℃687. For a resume of his work in connection with the transits of Venus see H. Woolf, The Transists of Venus (Princetion, 1959), esp. 98℃115.
Colin A. Ronan
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