Philippe de La Hire, physicien : philosophie mécanique, mécanique rationnelle, mécanique appliquée

Abstract

This article gives characteristics of Philippe de La Hire’s mechanics. By “mechanics” we mean both mechanical philosophy and rational and applied mechanics, and for each we analyze La Hire’s principles and methods. We show that his physics is in line with mechanical philosophy, especially that of Descartes, and he also seems to follow Gassendi and mechanistic chemists from the turn of the 17th and 18th centuries. Putting La Hire’s rational mechanics in perspective with that of some members of the French Academy of science, we shows that he favours the “Ancients” over the “Moderns” according to his own terminology. Generally speaking, La Hire favours geometry and “synthesis” rather than analytical developments. In statics, the Archimedean axiomatic remains a model, and we also show that he seeks to perfect machines by applying statics and geometry to them but he doesn’t propose tools quantifying their functioning and improvements, unlike some scholars of the time. Moreover, La Hire’s kinematics and dynamics depend on the geometry of the problem studied and on the possibility of geometrically interpreting Galilean propositions. The concepts of dynamics and the procedures of infinitesimal geometry in La Hire’s work echoed practices prior to the development of analytical mechanics.