Eugène CHEVREUL (1786-1889). L.A.S., [ca. 1880], to François - Lot 157

Eugène CHEVREUL (1786-1889). L.A.S., [ca. 1880], to François-Auguste Mignet; 3pages in-4 filled with small handwriting, on the letterhead of the Muséum d'Histoire naturelle (under glass). Very interesting, long letter from the scientific researcher to the historian. Chevreul has every confidence in Mignet and wants to ask him about "two points of my applications of the method, as I have defined it, to the sciences in your field". The 1st point concerns the explanation of facts. Chevreul starts with an anecdote told by de Thou about the future Henri IV playing dice "a few days before Saint-Barthélemy", and seeing "blood on the dice". According to Voltaire, "enemy of prodigy", this was "caused by the sun's rays falling on the eyelids at a certain angle". Beguelin, of the Berlin Academy, observed the phenomenon in 1771, but was mistaken "about the different effects of the phenomenon; for the explanation to be possible, it was necessary to know the law of simultaneous color contrast, which was not known until 1827". Chevreul, who had explained the phenomenon in 1839 without publishing it, showed the Académie des Sciences in 1876 "the comparative view of absolute black with material black; this comparative view is necessary to explain the phenomenon". But, before "publishing the whole of my research", Chevreul would like to know if any author before Voltaire had spoken of "the action of the sun on the eyes to produce the vision of red on black". As a 2nd point, Chevreul denounced a "great gap" in the teaching of philosophy; among the Greeks (Democritus, Pythagoras, Plato, Aristotle), it included "all the principles of human knowledge of the time", but "the science of molecular actions" was unknown to them, falling "within the scope of current physics and chemistry, whose consequences are considerable for knowing the truths accessible to the human mind. Since 1856, he has been working on "the definition of the word fact" through "the distinction I have made between the analysis of chemical synthesis and the analysis of mental synthesis". For him, "there is a general philosophy, the study of which [...] shows a perfect analogy between the categories of men of genius and of simple intelligence delivered to each of the branches of human intelligence, each endowed with a special philosophy". Chevreul follows this "long verbiage" with an overview of Marius Topin's book L'Homme au masque de fer; he has been struck by its "spirit of method", which he intends to cite "as a model to be imitated" in the appendix to his work: Résumé d'une histoire de la matière depuis la philosophie jusqu'à nos jours. By applying this method to the history of alchemy, he succeeded in "explaining the errors of the alchemists and those of eminent men who prefer phlogiston to Lavoisier's theory of combustion, the expression of truth"... And he concludes: "The final result of all my studies in the search for the unknown is 1° to define the facts relative to the object under study, 2° to interpret the facts. It is this interpretation that constitutes the theory of the natural sciences, when it has been subjected to experimental control"...