Towards the end of the eighteenth century there was an increased emphasis on quantitative precision in experimentation, together with a concerted effort to standardize methods and experimental devices in a way that would allow for reproducible results.10 An experimenter in such Baconian sciences as electricity, magnetism, chemistry, or early thermodynamics. sought to learn something novel from nature. Phenomena that did not lend themselves to familiar classification or fit standard theories were objects of qualitative studies and sources of aesthetic pleasure. Even the pages of the Philosophical Transactions of the Royal Society were filled with reports of marvelous phenomena and strange experiences, with the hope that an explanatory account would eventually emerge. The new experiments aiming at quantitative precision attempted, as Kant put it, to compel nature to answer our questions. The phrasing of the questions imposed a categorial system on communicable results. We will consider the attempts to incorporate thermodynamics and electrodynamics into a mechanistic system and its effect on the categorial core of the language of physics.
In the 1770s the young Laplace collaborated with Lavoisier in developing a chemical physics of heat, the caloric theory. This effort was later extended to hypotheses concerning short range forces and mathematical formulations that could be adjusted to explain heat, affinity, capillary action and other phenomena.11 This experimental and theoretical work conditioned his transformation of atomism. Descartes, Boyle, and with qualifications, Newton put atomism on an ontological foundation, buttressed by conceptual arguments. The properties of ultimate corpuscles must be all and only the properties of matter as such. Laplace changed this mechanistic atomism into atomistic mechanism. A foundational role is assigned to the principles of mechanics. Then mechanical hypotheses are introduced concerning particles and short range forces. Since the true intermolecular forces were unknown, Laplace sought confirmation through detailed experiments testing the ultimate consequences of his hypotheses. (Ibid. Vol. IV, p. 1009, vol. V, p. 466). Poisson coined the term 'physical mechanics' to characterize the difference between Laplace's work and Lagrange's analytic mechanics. (Taton, 1961, p. 102).
A simplified schematic outline of the development of thermodynamics supplies a screen on which the incorporation of thermodynamic concepts into a mechanistic framework can be projected12. Epistemologically sophisticated scientists did not think that heat, a secondary quality, was part of physics. Only Baconian science treated it. In the late eighteenth century Joseph Black and Johan Wilcke, more or less independently,
10 A general survey of eighteenth physical experiments is given in Hall, (1954), chap. 12. Kuhn (1977, pp. 31-65) brings out the characteristics of and transition from Baconian science. The emphasis on new instruments and quantitative precision is developed in Feldman, (1985). Rueger (1997) illustrates the striking differences between the goals of Baconian and more quantitative experiments.
11 Thus in Laplace, 1825, vol. 5, pp. 113-132 he treated small spheres with forces proportional to r-2-. The value = 0 fit gravitation, while = -3 supplied a model for molecules in static equilibrium. A further assumption concerning short range intermolecular repulsive forces allowed the deduction of Mariottes's (or Boyle's) law, Gay-Lussac's law, and Dalton's law of partial pressures. Further assumptions about the heat of particles allowed him to deduce the correct result for the speed of sound in air. (Ibid., pp. 133-145).
12 This is based chiefly on Truesdell, 1980. For the Baconian phase see McKie and Heathcote.