Died: 12 May 1742 in Paris, France

**Joseph Privat de Molières**'s parents were Charles Privat de Molières and Martine de Robins de Barantane. He was born into an aristocratic Provencal family, the second of his parents sons. He was given a good educations at schools run by the Congregation of the Oratory. The Congregation of the Oratory of Jesus and Mary Immaculate, often called the Oratorians, was a Roman Catholic sect founded by Pierre de Bérulle in 1611 and approved by the Pope in 1613. It had a fine reputation for providing a good education with particular emphasis on the classical languages. Joseph studied at Oratorian schools in Aix, Marseilles, Arles and Angers. At the last of these schools he studied under Charles-René Reyneau from 1698 until 1699. After the death of his elder brother, Joseph was expected to devote his life to running the affairs of his family. He chose, however, against his parents wishes, an ecclesiastical life and entered the Congregation of the Oratory in 1699.

His first posts were teaching in schools belonging to the Congregation of the Oratory, first at Saumur, then at Juilly and finally at Soissons. However he had a deep love of science in general, and mathematics in particular, and in 1704 he went to Paris to take up a more active scientific career. There he studied mathematics and physics with Malebranche until 1715. In 1723 he was appointed to a chair at the Collège Royal to succeed Varignon.

He argued against Newton and for Descartes' view of physics although he knew Newton's to be the more precise. Of course, although we now accept Newton's ideas of gravitation without much thought, it is clear if one thinks about it for a while that the idea of action at a distance through a vacuum is absurd. Many around this time voiced such an opinion (Newton himself realised this was a weakness in his theories) but where Privat de Molières differed from other critics of Newton's theory of gravitation is that he attempted to make a mathematically sound theory based on the idea of vortices. Understanding the accuracy of the theory of gravitation, Privat attempted to bring Newton's calculations into the vortex theory of matter of Malebranche. The problem was Kepler's laws, easily explained by Newton, but the cause of real problems for Descartes' vortex theory of planetary motion. Nakata gives details of Privat's theory in [5]. In fact in a memoir written in 1733 Privat criticised Newton's theories for being too accurate saying that physical phenomena did not have geometrical precision:-

However it will happen that it is only approximately that the points of the vortex will have this force which depends on the square of the distance and thus the area they span will also be only approximately as the time; but this will simply be more in conformity with the astronomical observations; thus the mechanical forces of the vortex give us the astronomical laws as they are in effect with a better precision than the purely metaphysical forces of Newton which give those laws with too much geometrical precision.

Fontenelle, the secretary of the Academy of Sciences, agreed with Privat de Molières. He wrote in his annual report on the work of the Academy:-

M l'Abbé de Molières astutely criticizes Newton on his extreme precision; physical principles are not so precise when we come to apply them to phenomena.

Although his arguments were very effective particularly as he was able to incorporate a theory of electrical and chemical phenomena within his little vortices theory, eventually Newtonian physics came to the fore in France.

Privat de Molières published *Lecons de mathematiques* (1726), a work on the principles of algebra and calculus. His *Lecons de physique, contenant les éléments de la physique déterminés par les seules lois des méchaniques* (1734-1739), was a four volume work based on his lectures at the Collège Royal and contains details of the mathematical theory of his elastic "little vortices". He also published a series of Memoirs of the Academy and in several articles in the *Journal de Trevoux.*

Privat de Molières was honoured by being elected to the Academy of Sciences in 1721, and became a Fellow of the Royal Society of London in 1729.

**Article by:** *J J O'Connor* and *E F Robertson*

**August 2006**

[http://www-history.mcs.st-andrews.ac.uk/Biographies/Privat_de_Molieres.html]