Breaking with Balance: Why Did Descartes Need Such a Complicated Image of the Lever?

The Treatise on Mechanics is a short essay by René Descartes (1596–1650) that deals with the so-called ‘simple machines’ of mechanics, which can be used to facilitate the lifting of heavy loads. It contains five hand-drawn images of such machines, which include the inclined plane, pulley, and lever. Descartes did not much care for the Treatise. He thought it was incomplete and generally unfit for publication. His contemporaries disagreed, however. Roughly thirty years after it was written, the treatise was published in brief succession in English, French, and Latin editions. Here, I assess the importance and novelty of the treatise with respect to the works contemporaneous readers would have compared it to: available treatises on the simple machines. We will look particularly at what these works tried to achieve, and how they went about their business. Although they do not seem to stand out at first sight, Descartes’s images have a number of particularities that set them apart from earlier works on the machines. I show that these particularities are bound up with a methodological choice by Descartes, namely his rejection of the convention of explaining the simple machines in terms of weights in equilibrium, and his introduction of the notion 'force'. At the end of this chapter. I address the paradoxical nature of Descartes’s force: on the one hand it is central to his mechanics, while on the other, it is strikingly absent in his images.