Georges-Louis Le Sage

In his early youth Le Sage was strongly influenced by the writings of the Roman poet Lucretius and incorporated some of Lucretius' ideas into a mechanical explanation of gravitation, which he subsequently worked on and defended throughout his life. Le Sage wrote in one of his cards, that he developed the basic features of the theory, which was later called Le Sage's theory of gravitation, already in 1743. Then on 15 January 1747 Le Sage wrote to his father:

Eureka, Eureka. Never have I had so much satisfaction as at this moment, when I have just explained rigorously, by the simple law of rectilinear motion, those of universal gravitation, which decreases in the same proportion as the squares of the distance increase.[7]

The first exposition of his theory, "Essai sur l'origine des forces mortes", was created by him in 1748, but was never published. In 1756 one of Le Sage's expositions of the theory was published,[8] and in 1758 he sent a more detailed exposition of the theory to another competition of the Academy of Sciences. In this paper, entitled "Essai de Chymie Méchanique",[9] he tried to explain both the nature of gravitation and chemical affinities. He shared the prize with one other entrant, but his theory of cohesion never gained acceptance, and only the gravitational portion of the theory was found to be of interest by a few of his contemporaries, including Euler. The exposition of the theory which became accessible to a broader public was "Lucrèce Newtonien" ("The Newtonian Lucretius"), in which the correspondence with Lucretius' concepts was fully developed.[10] Another exposition of the theory was published from Le Sage's notes posthumously by Prévost in 1818, and was called "Physique Mécanique de George Louis Le Sage", but it does not contain anything which was not published in the earlier papers.[11]

Le Sage was not the first to propose what is now called "Le Sage's theory of gravity". Those who had described the theory previously include Fatio, Cramer, and Redeker. The extent to which Le Sage was influenced by these predecessors is a matter of controversy.

The theory now called "Le Sage's theory of gravity" was originally proposed in the 1690s by Nicolas Fatio de Duillier, a friend of Sir Isaac Newton and Christiaan Huygens. Fatio was a well-known Swiss personage, and the kinetic theory of gravitation was his most notable scientific contribution, to which he devoted much of his life. Le Sage said that he heard of Fatio for the first time through his father, because his father had heard the prophecies of the cevénots (camisards), and told him that Fatio was among those prophets. Le Sage's father was well acquainted with the scientific fields in which Fatio worked, and he tutored Le Sage in the sciences. Nevertheless, Le Sage later claimed that his father never told him that Fatio had created a theory of gravitation essentially identical to his own. (Le Sage also admitted that he had a pathologically bad memory, so it is unclear if his recollection is accurate.) In any case, Le Sage stated that he knew nothing of Fatio's theory until he was informed by his teacher Gabriel Cramer in 1749.

A few years after Fatio's death (which occurred in 1753), Le Sage began trying to acquire Fatio's papers to – according to his own words – rescue them from oblivion, and also for a treatise he planned to write on the history of theories of gravitation. One of Fatio's papers was sent to Le Sage by Abauzit in 1758, and other papers were acquired by Le Sage in 1766, 1770 and 1785. He also started a biographical note on Fatio, although he did not complete it, and he tried without success to publish some of Fatio's papers. The Geneva manuscripts were deposited in the library of Geneva by Prévost after Le Sage's death and are still there.

Le Sage wrote to Lambert in 1768:[12] "Nicolas Fatio de Duillier had created a theory in 1689, which is so similar to mine, that it only differed in the elasticity, which he has given his intensely agitated matter". There he outlined the great similarity of the theories, but incorrectly claimed that Fatio assumed elastic collisions, even though the loss of speed of the gravitational corpuscles was explicitly stressed by Fatio as a crucial element of his theory. Le Sage sent in a letter to Boscovich the beginning of Fatio's Latin poem (modeled on Lucretius) on the subject of his theory of gravitation, and told him that he wanted to publish it, but Boscovich did not agree, arguing that it would be too hard for most people to understand if it is published in Latin.

Le Sage was worried about the possibility that people might think he had gotten the idea for the gravitation theory from Fatio, because he went to the trouble of making a "certificate", and having it signed by the mathematician Pfleiderer and the astronomer Mallet (two friends of Le Sage), stating that, except for a copy made by Abauzit in 1758, Le Sage saw no papers of Fatio before 1766, and in these papers there was nothing which was not developed by Le Sage in a more detailed way.

In the "Physique Mécanique" published by Prevost after Le Sage's death, Fatio is mentioned in connection with the net structure of matter, but it goes on to claim that he (Le Sage) had developed the idea of the net structure already in 1763, before he was in possession of Fatio's original papers. However, according to Zehe's description of the Abauzit manuscript from 1758, this paper contains Fatio's description of the net structure of matter. In the same paper, Le Sage repeated the incorrect claim that Fatio assumed "elastic" collisions – and therefore did not really provide a valid explanation of gravity. Zehe attempted to account for Le Sage's puzzling claims that Fatio assumed "elastic" collisions by speculating that Le Sage must not have studied Fatio's papers very closely.

In general, Le Sage and Prévost claimed that Le Sage's theory was superior to that of Fatio, but a more recent and detailed analysis of Fatio's paper by Zehe shows that it is Fatio's theory which is more developed.

According to Le Sage, after creating his first essay on gravitation, he was informed in 1748 by Firmin Abauzit about a very similar theory of Gabriel Cramer, who happens to have been Le Sage's teacher in Geneva. In later years Le Sage responded in two different ways to charges that his ideas on gravitation were only the result of studying Cramer's papers. First, he argued that his first essay was written before he knew of the theories of his predecessors. Second, he argued that even if he knew about Cramer's theory, it makes no difference, because Cramer's theory is too vague and scientifically not valuable. Le Sage did, however, accuse Cramer of plagiarising Fatio's theory. (Fatio himself had made the same accusation.)

In 1751 Le Sage also became aware of Franz Albert Redeker's theory. Le Sage began to write a history of theories of gravitation, in which he intended to describe the theories of Fatio and Redeker, but he never finished it.

Although Le Sage acknowledged that he was not the first one to propose such a theory, he always said that he was the first one who ever drew all consequences from the theory, even after coming into possession of Cramer's, Fatio's and Redeker's papers. For example, in his "Lucrece Newtonien" (1782) Le Sage did not mention any of his predecessors by name. He merely stated that it was "likely" such a simple idea had occurred to others previously, but if so, they had "presented it in a vague and ill-assured fashion".[13] He went on to ask rhetorically why none of these supposed predecessors (of whom he professes to have no definite knowledge) "pushed these consequences to their conclusion and communicated their research". He suggested that the answer was that they had no clear view of the subject, had not firmly grasped the principles of the theory, had allowed themselves to be seduced by specious sophisms, had bowed to the authority of great names, or had "lacked sufficient love of truth or courage of their convictions to abandon easy pleasures and exterior advantages in order to devote themselves to researches at the time difficult and little welcome.".[14]

Prévost praised his friend Le Sage for "scrupulously giving credit to his predecessors in all of his writings". However, although he sometimes referred to those predecessors, he often spoke in a derogatory way about them – see his comments in "Lucrece Newtonien", and his appraisal of Cramer as too vague and scientifically not valuable. Lord Kelvin and Aronson repeated Prevost's praise, based only on Prevost's account.