Abstract
The story of how Perrin’s experimental work established the reality of atoms and molecules has been a staple in (realist) philosophy of science writings (Wesley Salmon, Clark Glymour, Peter Achinstein, Penelope Maddy, …). I’ll argue that how this story is told distorts both what the work was and its significance, and draw morals for the understanding of how theories can be or fail to be empirically grounded.
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Notes
Brush (1976, p. 245): “In retrospect it seems clear that the criticisms of the kinetic theory in this period were motivated not primarily by technical problems, such as specific heats of polyatomic molecules but, rather by a general philosophical reaction against mechanistic or 'materialistic' science and a preference for empirical or phenomenological theories as opposed to atomic models”. (See further Nyhof 1988).
Maddy 2007, p. 72; But the first sentence contrasts starkly with the quick history she gives at other points: “atomic theory was well confirmed by 1860 and even more so by 1900” (p. 94). The tensions in her account of the history can be highlighted by Peter Clark’s survey of the fortunes of the atomic theory after 1860, and especially its status, deplored even by Planck, in the last two decades of that century. See further Liston (2007).
(Notice her odd use of “empirically adequate” in the last sentence, as compatible with failing empirical tests!) Maddy has a lengthy analysis of the episode in Naturalism in Mathematics, on which she relies in her later writings. On p. 306 of Second Philosophy she recounts quickly how she presented the case earlier in the book : “What is our Second Philosopher to make of this? The first and most fundamental unobservables are atoms, and we've seen (in I.5 and I.6) that the Second Philosopher takes Perrin's experiments on Brownian motion, confirming Einstein's theoretical predictions, as compelling evidence for their existence. Van Fraassen disagrees, insisting that no evidence can do this job, but unlike Stroud's skeptic, he presents no general argument for this stance. In the absence of such an argument, faced with the bare claim that atomic theory is empirically adequate but not necessarily true, the Second Philosopher might well take heart: van Fraassen appears to occupy the position of Poincaré and Ostwald ín 1900, a position she finds sound. Perhaps he can be persuaded, as they were, by a careful review of the new evidence of Einstein and Perrin! If not, perhaps he will explain why her faith in that evidence is misplaced; perhaps there is a weakness she hasn't noticed.”
Salmon (1984, p. 221), Glymour (1975, p. 409, note 12). Achinstein (2001) criticizes these accounts of Perrin’s reasoning, and offers his own ‘legitimation’—surprisingly, the premises he lists include a prior probability of at least ½ for the atomic hypothesis, and the conclusion is only that it is “greater”. Maddy takes for granted that Perrin’s reasoning and results do legitimate the conclusion, and does not offer a competing account to these.
The claim of empirical adequacy is like the claim of truth in going far beyond what our evidence could establish, for it entails that there are no phenomena anywhere in the universe or its history that contradict the theory. Since truth and empirical adequacy are on a par in that respect, how could that possibly be what is at issue between empiricist and realist? The debate between empiricists and scientific realists is not over the reality of unobservable entities, but over the telos of scientific activity. (What is true is that the debated questions would be moot, given an epistemology that would entail that the existence of unobservable entities—or conversely, that the empirical adequacy of a theory but not its truth—could be established on the basis of the evidence. Observing this distinction would help to alleviate the Naturalist Native’s confusion.)
Perrin took a definite side in a live controversy, though one that was already being overtaken by the radical conceptual departures from classical mechanics at that time (in which Perrin took no part). The difficulties of the kinetic theory between 1880 and 1905 are graphically described by Clark (1976, p. 82–88), and while his philosophical take on this period is challenged by Nyhoff (1988) and their dispute evaluated critically by De Regt 1996, the role and impact of those difficulties on scientific research in that period are not challenged.
The quote is from Ostwald, cited by Peter Clark (1976, p. 77), whom I follow in this passage.
See Mach (1883, p. 264–266) and its discussion by Duhem (1996, p. 121–122); Poincaré (1905, p. 89–110).
I will make this more precise below. It is not inappropriate, I think, to relate this to the older term “coordination” of Mach, Schlick, and Reichenbach; see my (2008), Chap. 5.
It is not the case that a logically weaker theory is automatically better confirmed or better supported by the evidence. The weaker theory may not be informative enough to allow for the design of a test. So for example the mere hypothesis of atomic structure, taken by itself, is not a well-tested theory (or tested at all!), though it is part of well-tested theories.
Pages 121–122 of his (1963) first published in German as Philosophie der Mathematik und Naturwissenschaft in 1927. This is quoted in Glymour (1980, p. 50) and discussed there, though it is not clear just how Glymour connects what Weyl writes with Glymour’s own central concern, which was confirmation of hypotheses relative to theories.
For detailed discussion see especially de Regt (1996), but it is also discussed by Gardner 1979, Clark 1976, p. 82–88, and Nyhoff (1988). We should note that at the time of Perrin this anomaly did not disappear, it was a main topic at the first Solvay Conference in 1911 where Perrin presented his results. In fact, there continues to be a voluminous literature on specific heat anomalies, for example at very low temperatures, but at present the problem they present is treated as ‘normal science’.
In his 1860 British Association Report, quoted Nyhoff (1988, p. 94).
This is the entire quote as given and discussed on Gardner 1979:19.
Page 246 in Dumas (1839) (lecture delivered 1836). I quote here the translation in the review, Pierson (1976, p. 135).
This was translated into English within the year as the book Brownian Movement and Molecular Reality. Although less historically and technically informative on some level, and on the other hand less explicit with respect to Perrin’s own interpretation of his results, it is much closer to the actual work than his later book Atoms (1913).
A gram-molecule of a substance is the mass of this substance which in the gaseous state occupies the same volume as 2 grams of hydrogen measured at the same temperature and pressure.
Here the philosophical literature is not always in accord with Perrin’s own account. As I shall discuss below Perrin (1910) presents his own research entirely before beginning part III with “ But another experimental advance was possible, and has been suggested by Einstein at the conclusion of the very beautiful theoretical investigations of which I must now speak” (1910, p. 51). Compare to this the order of presentation in Maddy (2000, p. 139–140 or Maddy 2007, p. 72, noting also the omitted background of initial experimental setbacks for Einstein’s work (Clark 1976, p. 97).
In 1926 Perrin received the Nobel Prize in physics, "for his work on the discontinuous structure of matter, and especially for his discovery of sedimentation equilibrium". The presentation speech by Professor Oseen of the Royal Swedish Academy of Sciences included the diagnosis “The object of the researches of Professor Jean Perrin which have gained for him the Nobel Prize in Physics for 1926 was to put a definite end to the long struggle regarding the real existence of molecules.” Such pronouncements are important for the historian, to indicate the terms in which such episodes were discussed, but we must always keep in mind that these words do not come in the context of a philosophy seminar, where our distinctions are made, or the conceptual problems are disentangled in the way we do.
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Acknowledgements
My thanks to the commentary by Helen Longino and the discussion at the Oberlin symposium; research for this paper was supported by National Science Foundation Senior Scholar Award SES-0549002.
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van Fraassen, B.C. The perils of Perrin, in the hands of philosophers. Philos Stud 143, 5–24 (2009). https://doi.org/10.1007/s11098-008-9319-9
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DOI: https://doi.org/10.1007/s11098-008-9319-9