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Lagny, Thomas Fantet de

1. Dates
Born: Lyon, 7 Nov. 1660
Died: France, 11 Apr. 1734
Dateinfo: Dates Certain
Lifespan: 74
2. Father
Occupation: Government Official
Pierre Fantet was a royal official in Grenoble. Lagny's mother was the daughter of a physician.
The "de Lagny" in his name comes from a property he (the scientist) acquired.
No information on financial status.
3. Nationality
Birth: French
Career: French
Death: French
4. Education
Schooling: Toulouse
He studied initially under a paternal uncle, then with the Jesuits in Lyon, and ultimately at the Faculty of Law in Toulouse for three years. There is no mention of a degree.
5. Religion
Affiliation: Catholic (assumed)
6. Scientific Disciplines
Primary: Mathematics
He is remembered for his contribution to computational mathematics. From 1687 to 1733 he published seven works.
7. Means of Support
Primary: Patronage, Government
In 1686 he was a tutor in the Noailles family at Paris.
In 1695 he was named an associate of the Académie Royale des Sciences.
In 1697 he was appointed professor of hydrography at Rochefort. (There are several Rocheforts in France. One is a port at the mouth of the Charente, a bit south of La Rochelle. Colbert created a shipyard there. Elsewhere I found a reference to an institute of hydrography there in the 18th century.) I surmise that this was a form of governmental employment.
From 1716 to 1718 he was the deputy director of the Banque Générale.
He became a pensionnaire of the Academy in 1719, and retired in 1733.
He was librarian of the Bibliothéque du Roi, but I don't know the years.
8. Patronage
Types: Aristrocrat, Court Official, Government Official
He was a tutor in the Noailles family. In 1716 his former pupil, the Marechal Duc de Noailles, president of the Conseil des Finances of the regency, called upon him to assume the deputy directorship of the Banque Générale.
In addition to the Duc de Noailles, Fontenelle also mentions as Lagny's particular friends the Chancellor (whoever he was then) and the Duc d'Orleans.
In one account the Abbé Bignon named him to the hydrography position. In NBG (apparently following Fontenelle) it was the Duc d'Orleans who named him. The two are not necessarily at odds; the abbé might have moved the duc to action. Lagny's nomination to the Académie in the late 90's certainly implies that he had the Abbé Bignon's favor. (I list Bignon as a governmental official.)
9. Technological Involvement
Type: Applied Mathematics
He is known for his contributions to computational mathematics.
I am not sure about that position in hydrography, but we found no references to active involvement in this field (cartography).
10. Scientific Societies
Memberships: Académie Royal des Sciences, 1695-1734, Royal Society
The Index biographique de l'académie lists the steps of his membership.
1696, académicien géomètre, académicien externe.
1699, associé géomètre, premier titulaire.
1699, associé mécanicien (replacing Sauveur)
1719, pensionnaire surnuméraire.
1723, pensionnaire géomètre (replacing Varignon)
1724, sous-directeur.
1725, directeur.
1733, pensionnaire vétéran.
  1. B. de Fontenelle, "Éloge de M. de Lagny," in Histoire de l'Académie...pour 1734, (Amsterdam, 1738), pp. 146-55.
  2. Index biographique de l'Académie des sciences, p. 320.
  3. Nouvelle biographie générale, 28, 825-6.
  4. Not consulted: Jean-Baptiste Duhamel, Regiae scientiarum academiae historia, (Paris, 1698), pp. 430-2. Microprint Q111.L2 no. D202 There is something wrong with this reference; there is no page 430 in this work.
Compiled by:
Richard S. Westfall
Department of History and Philosophy of Science
Indiana University

Note: the creators of the Galileo Project and this catalogue cannot answer email on geneological questions.

©1995 Al Van Helden
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