Le Monnier, Louis-Guillaume
Le Monnier, Louis-Guillaume
(b. Paris, France, 27 June 1717; d. Montreuil, France, 7 September 1799)
Le Monnier was the son of Pierre Le Monnier, professor of philosophy at the Collège d’Harcourt and member of the Académie des Sciences; his older brother was the distinguished astronomer pierre Charles Le monnier. Le Monnier’s scientific career was quite unusual. He is considered a botanist because this was the category of his membership is the Académie Royale des Sciences and, later, of his associate membership in the Institute, and because he was a professor at the Jardin du Roi. Yet on the basis of his very slight written work, which dates mainly from his youth, the title of physicist would be much more appropriate.
In 1739, at the age of twenty-two, le Monnier accompanied Cassini de Thury and Lacille on a mission to extend the meridian of the observatory of Paris into the South of France. His publications from this time (in Suite des mémoires de l’ Académie  contain accounts of purely physical experiments (observations of mercury in barometers in the mountains of Auvergne, in the Cabugiys, and elsewhere), descriptions of mines and mineral springs, adn the results of his botanizing.
It was with the publication of the manuscript ontaining his observations made in the South of France that le Monnier started his botanical career. In the province of Berry he noted diseased wheat on which the growths of ergot were an inch and a half long. He collected plants and drew up floras, some of twenty pages; for Berry, the mountains of Auvergne, Roussillon, and the mountains of the dioces of narbonne. He noted interesting ecological trends, finding similarities between the mountain plants and the plants of Lapland described by Linnaeusl. Although he did not publish anything after 1752, he continued his work as a botanist; the evidence can be found in the archives of the Museum of Natural History and of the Academy of Sciences.
In 1741 Le Monnier presented a memoir to the Academy entitled “Sur le rapport de différents degrés de fluidité des liquides.” Utilizing an original method, he presented measurements of the flow-times of a series of liquids through the same orifice. Le Monnier pointed out the importance of the “specific gracity” of these liquids. In 1744 he carried out analyses—simultaneously physical, chemical, and medical—of the mineral waters of Mont d’Or and Barège.
In 1746, following the famous Leyden jar experiment, he published “Recherches sur la communication de l’électricité.” Simplifying Musschenbroek’s apparatus, he verified the facts previously reported and established important new results: conducting bodies become charged with electricity as a function of their surface area, not of their mass; water is one of the best conductors of electricity. In this field le Monnier found himself the reval of the Abbé Nollet, who did not welcome any challenge to this authority. It was to Le Monnirt, “Aimant” and “Aiguille aimantée” in the first volume of the Envuvloédie. Furthermore Le Monnier communicatied to the Academy certain results “concerning the perfect resemblance recently observed between electric matter and that of thunder” ( “Observations sur l’électriicité de l’air” in Mémoires de l’Académie royale des sciences ), and six months later published his method of studying storms and his own findings, which confirmed Franking’s
In the Mémoires de l’Académie rooyale des sciences he signed his works “par M. Le Monnier, Médecin” to distinguish them from those of this father adn of fourteen years. It was both as a physician and as a botanist that he published his observations, “Sur les pernicieux effets d’une espéce de champignons appelsée par les botanistes, Fungus mediae magnitudinis totus albus Vsillsny n° 17.”
But all these efforts werte, for him, peripheral: his own science was botany, and we should be no more astonished to find him in 1745 taking Linnaeus botanizing in the forest of Fontainebleau with Antoine and Bernard de Jussieu than to see him as botanist at the Academy. If we are to believe G. Cuvier, “he could have been one of our most famous botanists,” but, prevented by timidity, he wrote nothing; this timidity was due to the “unjust criticisms to criticisms to which his first memoirs were subjected” -and Cuviier is un-doubtedly referring to the criticisms of the Abbé Nollet.
Le Monnier first practiced medicine in the hospital of Saint-Germain-en-Laye. Subsequently he was chief physician of the Hanoverian army (1756) and then first physician in ordinary both to Louis XV and to Louis XVI. He became first physician to the latter in 1788. Through kindness he also dispensed medical care to the poor.
His practical work as a botanist is worth mentioning. While still young he met Louis de Noailles at the latter’s garden. he enjoyed organizing de Noailles’s park, which contained rare trees and a botanical garden. One day there he fainted from excitement in the presence of Louis XV, who gave him a post as botanist and placed him in charge of the botanical garden of the Truanon. Owingn to his credit at court and at the Academy, Le Monnier obtained, through the help of diplomats and of botanists sent abroad on missions, a considerable number of plants which he raised in nurseries and which he gladly gave to plant-lovers. There are many examples of his work still in existence in Paris and he enriched French horticulture with many species of rhododendron and Kalmia, the long-flowered Mirabilis Jalapa, the pink-flowered locust, flowering dogwood (Cornus florida), and many other plants. He advocated the use of humus for plants liking an acid soil.
In Montreuil near Versailles, Le Monnier lived on the property of the Comtesse de Marsan, governess of the royal children. He had saved her life in a serious illness and her interest in botany helped him in his career.
He also an apartment in the Tuileries and on 10 August 1792, during the attack on his palace, his life was miraculously saved by an unknown individual. Destitute, he retired to Montreuil, where he lived a miserable existence on the income from an herbalist’s shop which the opened. After the death of his wife in 1793 he was cared for with devotion by a niece, who eventually married him.
Original Works. Le Monnier published the following papers: “Monnier (M. Le) Médecin. Ses observations d’historie naturelle faites dans les provinces méridionales de la France pendant l’annee 1739,” in Suite des Mémoires de l’Académie (1740), 111-235; “Sur le rapport des différences degrés de fluidité des liquides,” in Histore de l’Académie des Sciences (1741), 11-17; “Examen des eaux minérales du Mont d’Or,” in Mémoires del’Académie des Sciences (1744), 157-169; “Recherches sur la communication de l’électricité,” ibid. (1746) 447-464; “Examen de quelques fontaines minérals de la France,” ibid. (1747), 259-271; “Sur les pernicieux effects d’une espece de champignons, appelée par les botaniests, Fungues mediae magnitudinis totus albus Vaillant n° 17,” ibid. (1749), 210-223; and “Observations sur l’électricité de l’air,” ibid. (1752) 233-243. He also wrote the articles “Aiguille aimantee” and “Aimants” for Encyclopédie ou Dictionnaire raisonné des Sciences, des Arts et des Metiers, I (1757) 199-202 214-223. A large number of MSS are preseved in the Bibliothèque Centrale of the Muséum d’ Histoire Naturelle.
II. Secondary Literature. Two early biographies are G. Cuvier, “Notice sur la vie et les ouvrages du Cen Lemonnier,” in Mémoires de l’institut National des Science et des Arts, 3(an IX), 101-117, and A.N. Duchesne, “Éloge historique du Cit. Lemonnier, Médecin,” in Magasin encyclopédique (1799), 489-500.