César-François Cassini de Thury

César-François Cassini de Thury (17 June 1714 – 4 September 1784), also called Cassini III or Cassini de Thury, was a French astronomer and cartographer.

Cassini de Thury was born in Thury-sous-Clermont (Oise), the second son of Jacques Cassini and Suzanne Françoise Charpentier de Charmois. He was a grandson of Giovanni Domenico Cassini, and would become the father of Jean-Dominique Cassini, Comte de Cassini.

In 1739, he became a member of the French Academy of Sciences as a supernumerary adjunct astronomer, in 1741 as an adjunct astronomer, and in 1745 as a full member astronomer.

In January, 1751 he was elected a Fellow of the Royal Society.

He succeeded to his father’s official position in 1756 and continued the hereditary surveying operations. In 1744, he began the construction of a great topographical map of France, one of the landmarks in the history of cartography. Completed by his son Jean-Dominique, Cassini IV and published by the Académie des Sciences from 1744 to 1793, its 180 plates are known as the Cassini map (fr).

The post of director of the Paris observatory was created for his benefit in 1771 when the establishment ceased to be a dependency of the French Academy of Sciences.

His chief works are: La méridienne de l’Observatoire Royal de Paris (1744), a correction of the Paris meridian; Description géométrique de la terre (1775); and Description géométrique de la France (1784), which was completed by his son ("Cassini IV").

César-François Cassini de Thury died of smallpox in Paris on 4 September 1784,