Pons, Jean-Louis

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(b. Peyre, Dauphiné, France, 24 December 1761; d. Florence, Italy, 14 October 1831), astronomy.

Although it started at an even lower level and remained even more narrowly restricted in its devotion to cometary observations, Pons’s career was quite similar to that of Charles Messier.

Born to a poor family, Pons received a very incomplete education that did nothing to prepare him to become the most successful discoverer of comets in the history of astronomy. That preparation began only when, after entering the service of the Marseilles observatory in 1789 as its concierge, he was instructed in astronomy by the directors of that establishment. Pons progressed rapidly, devoting himself primarily to practical observation; an increasing familiarity with the normal aspect of the heavens enabled him quickly to perceive slight changes. Combined with excellent eyesight and great patience, this ability equipped him as a new “ferret of comets“his first discovery of such a celestial object—which he shared with Messier— occurred in July 1801. Curiously, this discovery was also Messier’s last. From then until August 1827 Pons rarely failed to discover at least one comet a year and found a total of thirty-seven during that twenty-six-year period.

These observations did not go unrewarded. In 1813 Pons was named astronome adjoint at the Marseilles observatory, and by 1818 he had become its assistant director. In the latter year he discovered three very small and tailless comets, for which feat the Académie des Sciences in Paris—aware that two of them would probably have gone unnoticed but for Pons—awarded him its Lalande Prize. One of these objects proved to be of extraordinary interest, for, pursuing Pons’s suggestion that this comet was the one he (Encke) had discovered in 1805, Encke calculated its elements, announced that it had a period of only 1,208 days, and predicted its return in 1822. That return, visible only in the southern hemisphere, was seen by Karl Rümker in Australia. Since this was only the second instance of a recognized return of a comet, its importance was acknowledged in 1823, when the Astronomical Society of London awarded one of its first gold medals to Encke—after whom the comet has come to be named, despite his own insistence that it should be called Pons’s Comet. The Society granted silver medals to Rümker and Pons, although technically Pons received his for the discovery of two new comets in 1822.

The latter two comets were not discovered at Marseilles, for, on the recommendation of F. X. von Zach, Pons had been called to Lucca in 1819 to become director of the new observatory created at Marlia by the Spanish infanta Maria Luisa, widow of the former King Louis of Etruria. There Pons added several comets to his list, for one of which—“la 26e ou la 27e qu’il a vue”—he shared another Lalande Prize with Joseph Nicolas Nicollet in 1821. This observatory was closed at the death of the Duchess Maria Luisa in 1824, and Pons, again due largely to Zach, was invited by Grand Duke Leopold II of Tuscany to become director of the Florence observatory in 1825. There he found seven more comets, three of which were acknowledged in 1827 in another joint Lalande Prize, shared with J. F. A. Gambart. Failing eyesight caused Pons to lose his position as the first announcer of comets after 1827 and, ultimately, to relinquish his observational duties a few months before his death.


I. Original Works. Exclusively an observer, Pons communicated his discoveries in informal letters to leading astronomers or learned societies rather than in formal papers. F. X. von Zach, especially, frequently quoted from these letters in his own communications to the Zeitschrift für Astronomie und verwandte Wissenschaften. He also published Pons’s “Observation d’une tache fort singuièdre qui a paru sur le soleil, le 23 déc. 1823“in his Correspondance astronomique, géographique, hydrographique et statistique, 9 (1823),603.

II. Secondary Literature. The only treatments of any extent are those by René Alby in J. F. Michaud, ed., Biographie universelle, new ed., XXXIV, 62–63; and by Elizabeth Roemer, Jean Louis Pons, Discoverer of Comets, Astronomical Society of the Pacific Leaflet no. 371 (May 1960). Useful information may also be gleaned from the prize-awarding speeches and comments: Henry Thomas Colebrooke, “On Presenting the Silver Medal to M. Pons,” in Memoirs of the Royal Astronomical Society, 1 (1822), 513–514; and Procés-verbaux des séances de l’Académie tenues depuis la fondation de l’Institut, jusqu’au mois d’août 1835, 10 vols. (Hendaye, 1910–1922), VI, 433; VII, 166–167; VIII, 549. Finally, since he had become an associate of the Royal Astronomical Society, that body’s publications acknowledged his death with brief biographical notices: Memoirs of the Royal Astronomical Society, 5 (1833), 410–411; and Monthly Notices of the Royal Astronomical Society, 2 , 68.

Seymour L. Chapin