"As a community, we are sometimes forgetful of the history of physics. Students often believe that progress in physics is a smooth road without controversy. New theories are not accepted without a fight. We should remember that the molecular kinetic theory was accepted only after many bitter fights. As Ostwald said (see Ref. 6), it was the work of Einstein and Perrin that convinced him of its validity. We hope that this paper will serve as a reminder of this history."
From Newburgh, Einstein, Perrin, and the reality of atoms: 1905 revisited
The history of thermodynamics and statistical mechanics (TSM) is a vast subject. How does one even begin to organize one's approach to studying it? One can look at the history of how physicists conceptualized links/analogies or disanalogies between TSM and other areas of physics. Or one can look at the role mathematics played within TSM's historical development, or on the interplay between theoretical advances and empirical observations.
However, the approach taken in this guide is to examine how commitment to, or rejection of, atomism played itself out in the history. Focusing on how commitment to atomism was in tension with macroscopic, fluidic/caloric, or aggregative views on the understanding of thermodynamic concepts provides one useful way to understand the history.
Here is a broad overview of the necessarily selective list of figures listed in the next part of the guide, where you will find many more resources if you want to delve further into TSM's history as well as a listing of works (including rare books) that Lehigh owns. A future iteration of the guide would benefit from some more about chemistry’s role.
Time and again in this history one finds questions arising about whether atomism is merely a convenient hypothesis for doing scientific work or whether it is actually an aspect of reality. The history of TSM provides a "laboratory" for grappling with the instrumentalism versus scientific realism debate in philosophy of science.
16th century to first part of 19 century
Galileo takes a “corpuscular” view of heat, at least in Il saggiatore (The Assayer), that is related to his critique of Aristotelianism. Ariew Descartes Among the Scholastics.
"In his endeavor to learn more about the secret workings of nature, Bacon came to the conclusion that the atomist theory could not provide sufficient explanations for the “real particles, such as really exist” (Bacon IV , 126: Novum Organum, II.viii), because he thought that the immutability of matter and the void (both necessary assumptions for atomism) were untenable." Klein Francis Bacon
Hooke’s work in his Micrographia, which records Hooke’s microscopic findings, has “corpuscular” dimensions. The early modern drive to understand the world mechanistically motivated an interest in microscopes, though the latter proved unhelpful in establishing the existence of atoms. Luthy Atomism, Lynceus, and the Fate of Seventeenth-Century Microscopy
Fenby (Heat: Its measurement from Galileo to Lavoiser) draws a distinction between two theories about heat, which he takes to help organize views on heat up to mid-century 19th century.
. …Material theories. These have their origin in the doctrine of the four elements (earth, water, air, fire), which is generally credited to Empedocles. The culmination of this view was caloric, the matter of fire, and Lavoisier's inclusion of this substance in his table of elements … In the second half of the 18th century, there was a widespread belief that heat was an imponderable fluid; sometimes this fluid was assumed to be made up of particles which repelled one another but were attracted to the particles of ordinary matter.”
Mechanical theories. The view that heat arises from the motions of the constituent particles of matter also has a Greek pedigree. Its first "modern" adumbration was by Girolamo Cardano in the 16th century, and the idea was elaborated by Francis Bacon in his Novum Organum (1620). [But see the section of this guide about Bacon for literature about the complexity of Bacon's views .] Newton, in his Opticks, believed that heat may be caused by a "vibrating motion" of the constituent parts of bodies. The first mathematical expression of the mechanical view was that of Daniel Bernoulli in Hydrodynamica (1738); …. Lavoisier and Laplace, in discussing various opinions concerning the nature of heat … mentioned a mechanical hypothesis in which "heat is the vis viva [mass x velocity2] resulting from the imperceptible motions of the constituent particles of a body …". Given Lavoisier's preference for a material heat, this view was presumably that of Laplace,….
In the early 19th century Carnot helped to adumbrate the first and second laws of thermodynamics, despite holding to a caloric (fluidic) theory of heat. (Access Science biography)
Second part of 19th century
This time frame saw major advances in statistical mechanics and thermodynamics. It is fascinating however that the reality of atoms, which played such a huge role in the development of statistical mechanics, was so much in dispute or regarded merely as a useful hypothesis.
"Clausius took kinetic theory into a mature stage, with the explicit recognition that thermal energy is but the kinetic energy of the random motions of the molecules and the explanation of the first law of thermodynamics in kinetic terms. Clausius had been the first to formulate the Second Law of thermodynamics and was, later, to discover the hidden concept of entropy." Cercignani, The Rise of Statistical Mechanics
Maxwell and Boltzmann and Van der Waals
Maxwell developed a view in which “… molecules are mass points (therefore not hard spheres) interacting at a distance with a repelling force inversely proportional to the fifth power of the distance (these ficticious molecules are nowadays commonly called Maxwell molecules). In the same paper he gave a better justification of his formula for the velocity distribution function for a gas in equilibrium. With his transfer equations, Maxwell had come very close to an evolution equation for the distribution function, but this last step must be credited to Ludwig Boltzmann (1844–1906). The equation under consideration is usually called the Boltzmann equation and sometimes the Maxwell–Boltzmann equation (to recognize the important role played by Maxwell in its discovery).” Cercignani, The Rise of Statistical Mechanics
Klein (The historical origins of the Van der Waals equation) notes that Van der Waals and Maxwell at least at one point in their careers held what amount to a certain amount of reserve about atomism:
"Not so many years before Van der Waals wrote his thesis, James Clerk Maxwell had set to work on the kinetic theory, wondering whether “there is any so complete a refutation of this theory of gases as would make it absurd to investi- gate it further so as to found arguments upon measurements of strictly ‘molecular’ quantities before we know whether there be any molecules”. Maxwell’s skepticism did not keep him from the kinetic theory of gases; on the contrary, it gave him an added incentive for pushing the theory far enough so the question of molecular reality could be tested by its experimental consequences, particularly the unexpected ones. Van der Waals worked in the same spirit, as we shall see."
Boltzmann's own views about the actual existence of atoms appear to be a point of scholarly debate. See Wilholt Ludwig Boltzmann’s Mathematical Argument for Atomism (not electronically accessible at Lehigh).
“Josiah Willard Gibbs, in perfecting chemical thermodynamics and in establishing statistical mechanics, based his work on hypotheses which he believed to be specifically independent of the intimate structure of substances.” Fleck Atomism in Late Nineteenth-Century Physical Chemistry
Despite all the work on molecular theories, Chalmers notes that "In the late nineteenth century leading scientists such as Ostwald, Duhem and Planck were inclined to take thermodynamics as the model of how science should proceed, maintaining a secure and productive relationship with experiment whilst avoiding hypotheses of the kind involved in atomism."
"On February 18, 1867, Sir William Thomson, later to be Lord Kelvin, read before the Royal Society of Edinburgh a paper entitled " Vortex Atoms." Supported in a sketchy manner, the central assertion of the paper was that the theory of vortex motion, a recent development in theoretical hydrodynamics, "inevitably suggests the idea that Helmholtz's rings are the only true atoms." According to this view, atoms are nothing more than loci of a special type of rotary motion within a homogeneous aether pervading space, and matter, then, simply "a mode of motion." In the months and years that followed, Thomson developed the mathematical basis of his theory and, at the same time, was able to enlist in its behalf the support of many of his most distinguished colleagues. While seriously entertained as a credible scientific hypothesis in some circles as late as 1906, the year before Thomson's death, the vortex atom was eventually forgotten ..." Silliman.
20th century: the acceptance of atomism
Perrin’s work about Brownian motion was finally considered to have resolved the issue about the existence of atoms.
It is probably not widely known how took a very long it took for atomism to establish itself finally, with the work of Perrin. The article "Atomism from the 17th to the 20th Century" by Alan Chalmers in the Stanford Encyclopedia of Philosophy (a huge, free source of long articles about philosophical themes) concludes by saying “atomism, which began its life as speculative metaphysics, has become a securely established part of experimental science”. Maybe this is a case of philosophy driving science! But with science settling (more or less) the issue. (Here is a book that develops this theme: Chalmers, A. 2009, The Scientist's Atom and the Philosopher's Stone: How Science Succeeded and Philosophy Failed to Gain Knowledge of Atoms. )
Finally, the guide links to materials relating to the role of history of science in learning and teaching science. The history of TSM provides an excellent case study in how knowledge of the genesis of concepts in a particular field enliven one's understanding of it. Moreover, it leaves one wondering whether philosophical and historical understanding of the history of physics might provide one tributary (among others) leading to new advances.