Introduction

Throughout the nineteenth century there were two quite separate approaches to the problems posed by thermal and thermochemical phenomena. The first, the mechanical theory of heat, which developed into a fully-fledged phenomenological thermodynamics, was based upon two very general empirical laws, independent of any hypothesis as to the ultimate nature of matter. The second, the kinetic theory, on the contrary began with specific assumptions as to the constitution of matter, viz. that it was discrete, molecular, ultimately atomic, and that heat was a ‘concealed’ form of motion associated with the molecules of a substance.

The kinetic theory is now regarded (rightly) as one of the greatest achievements of nineteenth century physics. However, in the last decade of that century it was subject to severe attacks from some of the leading scientists of the day. Planck, for example, regarded the theory as faced with ‘insurmountable obstacles’ such that ‘every attempt at elaborating the theory has not only not led to new physical results but has run into overwhelming difficulties’. Similarly Ostwald saw in the theory ‘a superficial habit to cover up rather than promote actual scientific tasks by arbitrary assumptions about atomic positions, motions and vibrations’, which in his opinion did ‘great harm to science’.