César-François Cassini de Thury

César François Cassini de Thury ( born June 17, 1714 Thury -sous -Clermont, † September 4, 1784 in Paris. Cassini III also called ) was a French astronomer and surveyor.

Life

He was the son of Jacques Cassini and grandson of Giovanni Domenico Cassini, which is why he also called Cassini III. is called. César assisted his father in 1733 and 1734 in the survey of northern France, at the then controversial issue should be clarified whether the earth is flattened at the poles or at the equator.

The Cassini took the erroneous view that the pole radius is larger than the radius of the Earth at the equator, a view that has been disputed vigorously by Isaac Newton and other scientists such as Maupertuis. The Cassini data, which they won in the national survey, although seemed to support a flattening at the equator, but it was demonstrated that neither the one nor the other theory could be proved by the then uncertainty in the measurements. In order to clarify the facts expeditions to Peru ( Bouger, La Condamine, Godin ) and Lapland ( Maupertuis ) were sent. While Jacques Cassini his life from his view not moved away, César Cassini later moved to the correct view of Newton.

In 1739 and 1740 he conducted another, very accurate measurements of the country and published his results in 1744, now convinced of the flattening of the earth at the poles. These surveys were the basis for the first complete mapping of France in 18 sheets at a scale of 1:870 000, which appeared in the years 1746 and 1747.

For military reasons mandated King Louis XV. Cassini, much more accurate to map France in scale 1:86 400. The duration of this project was estimated at 20 years, but after six years, state funding has been stopped so that Cassini only with private funds and with the support of the French provinces could continue to work.

Because of these difficulties, the survey and the production of the card pulled out further, so that he could not live to see the completion of his life's work. His son Dominique Cassini led the production of the Carte de Cassini to an end. 1761 Cassini was made an honorary member of the Bavarian Academy of Sciences. The Academy commissioned Cassini 1761/1762 with the creation of multiple baselines in the Munich area around the National Survey of Bavaria to take shape.

Like his father and his grandfather was Cassini III. However, from 1771 director of the Paris Observatory, he could give of Astronomy no new impulses.

The asteroid ( 24103 ) Dethury was named after him.