Interesting. What presuppositons was he operating under? Did he assume a globe Earth and used the distance between SA and Paris according to that model?
Domenico Cassini was a surveyor and geodest as well as an astronomer.
Cassini’s talent as a surveyor was well known. In 1657 he was asked by none other than Pope Alexander VII (the pope who put Galileo's and other books on the Index) to resolve a dispute regarding the flow of the River Reno between Bologna and Ferrara that was causing flooding. For the next seven years Domenico Cassini was occupied with similar work around the Papal States, spending only a little of his time at astronomical studies.
While working for Pope Alexander VII, Cassini sent a letter to the Jesuit Riccioli recommending the Immaculate Conception be celebrated as a special feast day. This happened 200 years later in 1854 when Pope Pius IX made it a dogma.
King Louis XIV of France approved Cassini’s last great expedition. With the aid of his son Jacques Cassini (Cassini II) and others, he measured the arc of meridian from Paris north to Dunkirk and south to the boundary of Spain, and, in addition, he conducted various associated geodesic and astronomical operations that were reported to the Academy. Cassini knew that it would be virtually impossible to measure every kilometre of meridian from Pole to Pole. At best, a northern measurement would confirm a probable shape of the Earth. Consequently, they decided to measure where it was most convenient, restricting their efforts to Europe in the northern hemisphere.
The results, published by Cassini II in 1720, showed the length of a meridian degree north of Paris was 111,017 meters or 265 meters shorter than one south of Paris (111,282 meters). This suggested that if this trend occurred in the southern hemisphere, the Earth has to be a prolate spheroid, not flattened at the poles as Newton proposed, but slightly pointed, with the equatorial axis shorter than the polar axis, that is, kind of egg-shaped rather than orange shaped.
The Cassinis’ prolate spheroid, of course, was at odds with Newton’s oblate spheroid. Nevertheless, in spite of the Cassinian measurements, the British scientists, William Whiston, freemason John Theophilus Desaguliers, and John Keill continued to acclaim Newton’s theory of the Earth’s shape as the true one. Then, in 1732, Pierre Louis Moreau de Maupertuis joined Newton’s team to be followed by the prominent scientist Alexis Clairout. Indeed, such was their quest for a bulging Earth that they decided to try to falsify the observations and figures of the Cassinis and thus clear the way for a triumphant Newtonianism. To this end they decided they would conduct a new survey. This time though, they would measure two points on Earth where the differences would be greatest if it were an orange shape, at the Equator and at the Poles. In 1735, financed by King Louis XV this time, one group went to Peru under Pierre Bouguer and Charles Marie La Condamine and a year later another group went to Lapland under Maupertuis. The polar expedition - after the conditions nearly killed them - completed its mission by 1737. Measuring only one baseline, 14.3 kilometres long, they ‘found’ their bulge. On hearing this Voltaire dubbed Maupertuis:
‘“Marques of the Arctic Circle,” “dear flattener of the world and of Cassini,” and “Sir Isaac Maupertuis,” for his vindication of Newton.’
Poll
