Abstract

This paper deals with Descartes’s and Roberval’s attempts to devise and describe the center of agitation of a composite pendulum. This episode has received some attention in the recent literature. It is usually depicted as the first step in the development of a general procedure for establishing the center of oscillation of a pendulum. My aim is to explore the different physical concepts and assumptions which informed the two mathematical accounts of the composite pendulum. I will argue that force, agitation, heaviness, or resis­tance of air essentially meant different things for Descartes and Roberval. As a result, the physical phenomena covered by the two geometrical procedures were quite distinct, and both mathematicians envisaged different roles of these phenomena within their agenda of studying nature.