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The Dissertation sur la glace, written by Jean-Jacques Dortous de Mairan at the beginning of his career in Béziers and Bordeaux, then entirely revised thirty years later when he had become a reputable member of the Royal Academy of Sciences, was considered by his contemporaries as a major contribution on the subject. Proceeding from the formation of ice to the melting of ice, the whole range of relevant phenomena are studied, through numerous observations and experiments. The main concept that Mairan makes use of is that of subtle matter. By 1749, however, such theories were no longer well considered. This induced the author to add a preface defending system-mindedness. This preface did not fail in turn to attract the criticism of the Encyclopedists.