February 18th was the 345th birthday for French Astronomer & mathematician Jacques Cassini [1677-1756]. He was the son of the more famous Giovanni Domenico (Jean-Dominique) Cassini [1625-1712], who had discovered four moons of Saturn, plus the division in the rings of Saturn named after him.
Jacques was 14 years old when he successfully defended his thesis on optics at the Collège Mazarin in Paris, and was 17 years old when he was admitted to the French Academy of Sciences to begin his scientific career.
Like his father before him, Jacques was interested in both astronomy and geodesy. In astronomy he also followed his father in studying Saturn, and made serious contributions to the study of Saturn's moons & rings. Jacques Cassini's tables for the satellites of Saturn were the first published by anyone, in 1716.
In 1738, he was able to verify the proper motion of stars, first discovered by Edmund Halley in 1718. Halley made the discovery by comparing his own
But in geodesy, multiple survey expeditions convinced Cassini that the Earth was elongated at the poles (prolate), which we now know is not the case, and just about everybody else knew even then was not the case. But Cassini would not be deterred.
One possible explanation was that Cassini, along with many other French astronomers, refused to accept Isaac Newton's [1643-1727] theory of gravity (1687), because it was English, and accepting it brought their loyalty to France into question. Newton had predicted that Earth must be wider at the equator, than at the poles (oblate), so the French were simply not allowed to believe such an English idea. This anti-English attitude did in fact seriously delay the acceptance of Newton's physics in France.
Asteroid 24102 Jacquescassini is named in his honor.
https://en.wikipedia.org/wiki/Jacques_Cassini
https://mathshistory.st-andrews.ac.uk/. ... i_Jacques/ (Mathematical biography)
https://www.gettyimages.com/.../louis-x ... /526613874 (Image source)
