Einstein-Perrin dilemma on the Brownian motion (Avogadro's number) resolved? (Q6633329)

This paper begins with a review of the history of (the theory of) Brownian Motion. It then discusses the discrepancies between different methods for determining Avogadro's number, specifically between the value obtained by Perrin through the empirical study of Brownian motion and the value obtained by Einstein from Planck's radiation law (though the latter method is not discussed in detail). The author describes Einstein's suggestion that the discrepancy may be due to Perrin underestimating the size of the gamboge spherules whose Brownian motion through water he was tracking. From his experience with sugar solutions -- the topic of his PhD thesis -- Einstein expected the (hydrophilic) gamboge spherules to swell in the water and thus to be larger than in the dry state. This explanation was rejected by Perrin and his collaborators, and Einstein did not pursue the question further. In the final section of this paper, the author argues that later research -- in particular in the field of polymer science -- has vindicated Einstein.