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Cassini, Jacques [Cassini II]

1. Dates
Born: Paris, 18 February 1677
Died: Thury, Oise, 15 April 1756
Dateinfo: Dates Certain
Lifespan: 79
2. Father
Occupation: Scientist
Cassini was the son of Jean Dominique Cassini and Genevieve de Laistre. His father was a greatly esteemed astronomer, head of the Paris observatory, an academicien, and active in the cartographical projects of France.
It is clear that Jean Dominique Cassini became wealthy as the head of the observatory.
3. Nationality
Birth: France
Career: France
Death: France
4. Education
Schooling: No University
Began his studies at Family's home in Paris observatory.
Entered the College Mazarin. 1691, defended a thesis in optics under Varignon. Fontenelle wrote that Cassini, at the age of fifteen, dedicated a mathematical thesis to the Duc de Bourgogne. Probably his thesis in optics is meant.
1694, admitted as a student to the Académie des Sciences.
There is no record of any university or standard academic degree.
5. Religion
Affiliation: Catholic (assumed).
6. Scientific Disciplines
Primary: Astronomy, Cartography
Subordinate: Electricity, Physics, Optics
He travelled with his father through Italy, Flanders, the Netherlands, and England making numerous geodesic measurements as well as several astronomical observations.
He presented a new method for the determination of longitudes by means of the eclipses of the stars and planets by the moon.
In 1713 he took the position supporting the hypothesis of the elongation of the terrestrial ellipsoid. In his work, De la grandeur et de la figure de la terre (1722), he presented information confirming his hypothesis. In 1733-34 he undertook the determination of the perpendicular to the meridian of Paris from Saint-Malo to Strasbourg in order to defend his views against those of Desaguliers, Maupertuis, and Poleni.
In astronomy Cassini's primary interests were the study of planets and their satellites, the observation and theory of comets, and the tides. Cassini fought continually to defend the work of his father and to reconcile the facts of observation with the theory of vortices. The improvements of instruments and the appearance of new methods were not used to their full extent by this timid Copernican and convinced Cartesian.
He gave papers to the Academie on electricity, the recoil of firearms, barometers, and burning mirrors.
7. Means of Support
Primary: Government
1699, became an associate in the Académie.
1706, named maitre ordinaire of the chambre des comptes, despite only modest legal training.
Before 1710, took over from his father as head of Paris Observatory.
1712, suceeded his father as pensionaire of the Académie. Ten years before his death he became pensionnaire veteran at the Académie.
1716, designated magistrate of the cour de justice, he necessarily obtained title of advocat.
1722, awarded title of consieller d'etat.
8. Patronage
Type: Court Official
The details of patronage which led to distinctions above are not clear, but cannot, it seems, be independant from his father's position in the Académie and the Paris Observatory.
9. Technological Involvement
Types: Cartography, Instruments
Worked with his father (1700-1701) and himself later finished the measurement of the arc of the meridian through Paris.
As an astronomer he improved instruments; especially important was a new micrometer.
After 1740 he collaborated with his son, Cassini de Thury (Cassini III) on a map of France.
10. Scientific Societies
Memberships: Académie Royal des Sciences, Royal Society, Berlin Academy, Institute Bologna
Member of the Académie (1694-1756)--Associate, 1699; Pensionnaire, 1712.
While on his travels with his father he met Newton, Flamsteed, and Halley and became a member of the Royal Society, c. 1698.
  1. M. Prevost, "Cassini (Jacques)," Dictionnaire de Biographie Francaise, VII (Paris, 1956), cols. 1329-1330.
  2. Bernard de Fontenelle, "Eloge de M. Cassini," Histoire et mémoires de l'Académie des Science, 1756, pp. 134-47.
  3. Hoefer, Nouvelle biographie générale, (Paris, 1857-66).
  4. Michaud, Biographie générale.
  5. J.B.J. Delambre, Histoire de l'astronomie au dix-huitieme siecle, (Paris, 1827), pp. 250-75.
  6. I am astonished at how little literature I can find on this important man.
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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