**Charles Bossut**'s father was Barthélemy Bossut and his mother was Jeanne Thonnerine. Charles never knew his father for his died when he was only six months old. The arrangement which allowed him to be brought up in a reasonably affluent home was that his father's brother took over the role of his father and Charles was brought up in his home. He was educated at the Jesuit College of Lyon which he entered at the age of fourteen. There he was taught mathematics by Père Béraud who had already taught Montucla and inspired him to study mathematical physics. Montucla was five years older than Bossut and completed his studies at the Jesuit College of Lyon about the time that Bossut entered. Another famous mathematician also studied under Père Béraud at the College, namely Jérôme Lalande who was two years younger than Bossut so the two overlapped at the College.

Although his main interests were in mathematics, and particularly in mathematical education, Bossut continued in the Church after his studies at the Jesuit college, and took holy orders becoming an abbé. He was then properly addressed as the Abbé Charles Bossut. He was encouraged in his mathematical researches by d'Alembert, Clairaut and Camus. He became a student of d'Alembert and in that capacity was admitted to the Academy of Sciences as a 'correspondant' on 12 May 1753. Before this in 1752, at the age of 21, Bossut had been appointed professor of mathematics at the École du Génie at Mézières, the first school of military engineering which had been established at Mézières in 1748. (Lazare Carnot, himself a graduate of Mézières who studied there after Bossut had left, moved the school to Metz in 1794 where it was renamed the École Polytechnique). While at Mézières, Bossut transformed the quality and content of the courses. Among his students at Mézières were Borda and Coulomb. He also did fine research and won Academy prizes for his work on mechanics applied to ships and on resistance to planetary motion. It was a memoir of 1762 which won Bossut the Grand Prix of the Academy of Sciences for work on the resistance of fluids to the motion of planets. He also won the Grand Prix (or shared it) in 1761 and 1765.

Then in 1765 Monge was appointed to the École du Génie as a draftsman. Of course, in this post Monge was undertaking tasks that were not entirely to his liking, for he aspired to a position in life which made far more use of his mathematical talents. However the École du Génie brought Monge into contact with Bossut who encouraged him to develop his ideas on geometry. After Bossut left the chair of mathematics at the École du Génie at Mézières in 1768, Monge was appointed to succeed him in January 1769. C B Boyer writes:-

The letter is published in [5].On22January1769Monge wrote to his former mentor, the Abbé Charles Bossut, that he was composing a memoir on the evolutes of curves of double curvature, and he asked the abbé for an opinion on the originality and usefulness of the work. Bossut's reply has not survived; but the judgment evidently was encouraging, for in June of the same year there appeared in the J Encyclopédique a "Lettre de M Monge" containing a summary of his results. The theory of evolutes for plane curves had been presented by Huygens about a century earlier in connection with the study of pendulum clocks. The "Lettre" of Monge not only generalized the conclusions of Huygens to space curves, but added further discoveries, including the significant fact that the surface containing the centres of curvature of a gauche curve is developable.

Bossut is famed for his textbooks which were widely used throughout France. He wrote his first textbook *Traité élémentaire de méchanique et de dinamique appliqué principalement aux mouvements des machines* Ⓣ (1763) while at the École du Génie. He also published the more famous *Cours complet de mathematiques* Ⓣ in 1765. Although, as we indicated above, he left the chair of mathematics at Mézières in 1768, he remained as an examiner at the School until the it moved to Metz in 1794. He then essentially continued his role, becoming an examiner at the École Polytechnique.

The economist Turgot, Baron De L'Aulne, was appointed 'comptroller general' of France by Louis XVI on 24 August 1774. Among his first actions was the creation of a chair of hydrodynamics at the Louvre, where he himself had studied. Turgot's friend the Marquis de Condorcet, who he had appointed as Inspector General of the Mint, may well have influenced him to create the chair. Since Condorcet and Bossut were close collaborators it may have essentially been created for Bossut who certainly was appointed and filled it until 1780. In 1775 Bossut participated with d'Alembert and Condorcet in experiments on fluid resistance. Also during this period he was editing an edition of the works of Pascal which was published in five volumes in 1779.

He was later to collaborate with d'Alembert on the mathematical part of Diderot's *Encyclopédie méthodique* Ⓣ. Also later in his career he wrote *Méchanique en général* Ⓣ (1792) and his treatise on the history of mathematics in two volumes *Essai sur l'histoire générale des mathématique* Ⓣ (1802).

Bossut became somewhat of a recluse during the last years of his life. He had never married and had no close family. Although he seems to have come to dislike the company of people, he had been honoured for his work by many scientific academies. The academies of Lyons and Toulouse awarded him prizes, and he was elected to the St Petersburg Academy of Sciences as well as the academies at Turin and Bologna.

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

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