Jürgen Renn

The Challenging Images of Artillery

Princely families of old were in the habit of engaging historians who were charged with producing tailor-made histories, in which the achievements of these families received due attention. For a long time this, remarkably, was exactly what natural scientists also expected from their historians. As a matter of fact, from the point of view of developed science, the knowledge of a discipline is simply represented by the natural laws that define its object. It was accordingly a matter of course for its historians to concentrate solely on the question of who had discovered which of these laws when and in what manner. In this sense, the history of science is a biographically oriented, heroic history of the great discoverers and their discoveries (fig. 1).

Mental Models as Cognitive Instruments in the Transformation of Knowledge

The chapter is concerned with the epistemic structures of mechanical knowledge in its historical transformations. It describes these structures using the concept of mental models as cognitive instruments, which function as mediators between the realm of practice and experience on the one hand, and conceptual systems on the other. With the help of the concept of mental model, the chapter discusses how mechanical knowledge has emerged from experience in practical contexts and how it was transformed into theoretical and mathematically formalized knowledge systems. Focusing on one particular mental model, which describes the cognitive structure conceptualizing motion as being caused by forces, the chapter then follows its transformations in the long-term history of mechanical thinking. This so-called “motion-implies-force” model is rooted in intuitive, non-written mechanical knowledge. Over the course of history, the model was recruited, complemented, and transformed in the context of the use of mechanical tools and articulated in the work of practitioners dealing with machines, arms, ships, buildings, fortifications, and the like. Eventually, under specific cultural circumstances, this and other mental models were elaborated and integrated into mathematically formalized systems that were used, for example, in the explanation of terrestrial and celestial motions in early modern natural philosophy and the mathematical disciplines of European universities.

The Balance, the Lever and the Aristotelian Origins of Mechanics

The Mechanical Problems traditionally attributed to Aristotle is a short problem collection that also contains an ambitious project of reduction, which traces various mechanical devices back to the lever, the balance and the radii of a circle. This work is thus not just a collection of problems, but also the first theoretical mechanical treatise that has come down to us: Basic concepts of technical mechanics such as force, load, fulcrum are abstracted from an analysis of simple technology, and the workings of this technology are explained by arguments cast in syllogistic form. This chapter traces the origins of mechanical theory in this work and analyzes the form and structure of its argument. The key steps in the concept formation of basic mechanics carried out in this treatise are analyzed in detail. We focus on the special role of the balance with unequal arms in the early development of mechanics, on the interaction of various forms of explanatory practice and on their integration into systems of knowledge in the Peripatetic school.

Galileo’s Unpublished Treatises

Galileo’s last publication, his Discorsi e dimostrazioni matematiche intorno a due nuove scienze attenenti alla mecanica & i movimenti locali (1638), is widely considered to be one of the most influential contributions of early modern science to the emergence of classical physics. As the title of Galileo’s book indicates, he himself claimed to have established “two new sciences,” including a new science of motion which, from the perspective of classical physics, indeed turned the Aristotelean theory of motion, which had prevailed for hundreds of years, into an obscure medieval relic.

Conservation and Contrariety: The Logical Foundations of Cartesian Physics

The general theory of matter presented by Descartes in the second book of the Principia Philosophiae is the first well founded systematic physical theory of modern science; for it explicitly introduces the logical presuppositions necessary for a system of causal explanations of physical phenomena using equations. While it is true that Descartes himself takes very little advantage of the possibilities created by the introduction of these prerequisites (there is, for instance, very little mathematics, no formal equations, and few proportions in the Principia itself), he nonetheless determines basic requirements of such a system of explanations and provides conceptual instruments adequate for the formation of such a physical theory.

Proofs and Paradoxes: Free Fall and Projectile Motion in Galileo’s Physics

According to a well established view the work of Galileo marks the beginning of classical mechanics.1 His work does not yet represent the full fledged classical theory as it emerged in the contributions of Newton and others, but, following this widespread interpretation, Galileo did take the first decisive steps: he criticized and overcame the traditional Aristotelian world picture, he introduced the experimental method, he concentrated on a systematic and concise description of single phenomena rather than searching for their causes and elaborating an overarching philosophy of nature, and he succeeded in the mathematical analysis of some of the key problems of classical mechanics.2