Brit. J. Phil. Sci. 47 (1996), 31-62 Philosophy and the Kinetic Theory of Gases Henk W. de Regt ABSTRACT This article examines the role of philosophy in the development of the kinetic theory of gases. Two opposing accounts of this role, by Peter Clark and John Nyhof, are discussed and criticized. Contrary to both accounts, it is argued that philosophical views of scientists can fundamentally influence the results of their scientific work. This claim is supported by a detailed analysis of the philosophical views of Maxwell and Boltzmann, and of their work on the kinetic theory, especially concerning the so-called specific heat anomaly. It leads to the conclusion that the scientific development of the kinetic theory cannot be understood without taking into account the role of philosophy. 1 Introduction: two views on the role of philosophy 2 The philosophical views of James Cleric Maxwell 3 The philosophical views of Ludwig Boltzmann 4 Maxwell, Boltzmann, and the specific heat anomaly 5 Conclusion: evaluating the analyses of Clark and Nyhof 1 Introduction: two views on the role of philosophy The development of the kinetic theory of gases is a famous and well- documented episode in the history of science. Above all, the heated dis- cussions between Boltzmann and his adversaries Mach and Ostwald over the existence of atoms and the value of the kinetic theory have received wide attention in the literature (e.g. Hiebert [1971]; Blackmore [1972]; Brush [1976]). From these debates it is clear that different stances towards the kinetic theory and atomism corresponded with different philosophical positions. Broadly, those who rejected the theory and atomism tended to be positivists, while its defenders were more likely to be drawn towards realism. 1 There is, however, no agreement as to the nature of the inter- action between scientific and philosophical factors in the historical development of the kinetic theory. Two opposing views concerning the role of philosophy can be distin- guished. Some authors hold that the philosophical climate of the late nineteenth century changed in favour of positivism independently of © Oxford University Press 1996