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

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

and

cartographer Cartography (; from , 'papyrus, sheet of paper, map'; and , 'write') is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an imagined reality) can ...

Biography

Cassini de Thury was born in Thury-sous-Clermont, in the

Oise Oise ( ; ; ) is a department in the north of France. It is named after the river Oise. Inhabitants of the department are called ''Oisiens'' () or ''Isariens'', after the Latin name for the river, Isara. It had a population of 829,419 in 2019.< ...

department, the second son of Jacques Cassini and Suzanne Françoise Charpentier de Charmois. He was a grandson of

Giovanni Domenico Cassini Giovanni Domenico Cassini (8 June 1625 – 14 September 1712) was an Italian-French mathematician, astronomer, astrologer and engineer. Cassini was born in Perinaldo, near Imperia, at that time in the County of Nice, part of the Savoyard sta ...

, and would become the father of Jean-Dominique Cassini, Comte de Cassini. In 1739, he became a member of the

French Academy of Sciences The French Academy of Sciences (, ) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French Scientific method, scientific research. It was at the forefron ...

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 Fellowship of the Royal Society (FRS, ForMemRS and HonFRS) is an award granted by the Fellows of the Royal Society of London to individuals who have made a "substantial contribution to the improvement of natural science, natural knowledge, incl ...

. Cassini de Thury succeeded his father's official position in 1756 and continued the hereditary

surveying Surveying or land surveying is the technique, profession, art, and science of determining the land, terrestrial Plane (mathematics), two-dimensional or Three-dimensional space#In Euclidean geometry, three-dimensional positions of Point (geom ...

operations.Jonathan Powell, ''From Cave Art to Hubble: A History of Astronomical Record Keeping'', (Springer Nature Switzerland AG, 2019), 115 In 1744, he began the construction of a great topographical map of France, one of the landmarks in the history of

cartography Cartography (; from , 'papyrus, sheet of paper, map'; and , 'write') is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an imagined reality) can ...

. Completed by his son Jean-Dominique, and published by the

Académie des Sciences The French Academy of Sciences (, ) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French Scientific method, scientific research. It was at the forefron ...

from 1744 to 1793, its 180 plates are known as the Cassini map. The post of director of the

Paris Observatory The Paris Observatory (, ), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world. Its historic building is on the Left Ban ...

was created for his benefit in 1771 when the establishment ceased to be a dependency of the French Academy of Sciences. A letter and proposal sent by Cassini de Thury to the

Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...

in London instigated the Anglo-French Survey (1784–1790), which measured the precise distance and direction between the Paris Observatory and the

Royal Observatory, Greenwich The Royal Observatory, Greenwich (ROG; known as the Old Royal Observatory from 1957 to 1998, when the working Royal Greenwich Observatory, RGO, temporarily moved south from Greenwich to Herstmonceux) is an observatory situated on a hill in Gre ...

, by way of a trigonometric survey. His chief works are: ''La méridienne de l’Observatoire Royal de Paris'' (1744), an arc measurement correction of the

Paris meridian The Paris meridian is a meridian line running through the Paris Observatory in Paris, France – now longitude 2°20′14.02500″ East. It was a long-standing rival to the Greenwich meridian as the prime meridian of the world. The "Paris meri ...

( Dunkirk-Collioure arc measurement (Cassini de Thury and de Lacaille)); ''Description géométrique de la terre'' (1775); and ''Description géométrique de la France'' (1784), which was completed by his son (""). César-François Cassini de Thury died of

smallpox Smallpox was an infectious disease caused by Variola virus (often called Smallpox virus), which belongs to the genus '' Orthopoxvirus''. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (W ...

in Paris on 4 September 1784.

Works

*''La méridienne de l’Observatoire Royal de Paris'' (1744) *''Description géométrique de la terre'' (1775) *''Description géométrique de la France'' (1784) *

Bibliography

D. Aubin, ''Femmes, vulgarisation et pratique des sciences au siècle des Lumières : Les ''Dialogues sur l’astronomie'' et la ''Lettre sur la figure de la Terre'' de César-François Cassini de Thury'', Brepols (2020)

References

External links

List of online works
available on Gallica
Cassini map online on EHESS site

cartocassini site
gathers old maps and allows for various manipulations, notabl

Cassini map in Géoportail (IGN)

* ttps://bibnum.obspm.fr/ Paris Observatory digital library {{DEFAULTSORT:Cassini De Thury, Cesar Francois 1714 births 1784 deaths Giovanni Domenico Cassini Scientists from Paris 18th-century French astronomers 18th-century French cartographers Members of the French Academy of Sciences Fellows of the Royal Society Deaths from smallpox in France French geodesists

Biography

Works

Bibliography

See also

References

External links