Brownian motion and molecular reality : a study in theory-mediated measurement /
Smith, George E.(George Edwin),1938-author.
Seth, Raghav,author.
based on (work):Perrin, Jean,1870-1942.Les atomes.
"Legend has it that Jean Perrin's experiments on Brownian motion between 1905 and 1913 "put a definite end to the long struggle regarding the real existence of molecules." Close examination of these experiments, however, shows how little access they gained to the molecular realm. They did succeed in determining mean kinetic energies of particles in Brownian motion, but the values for molecular magnitudes Perrin inferred from them simply presupposed that those energies match the mean kinetic energies of molecules in the surrounding fluid. This presupposition became increasingly suspect between 1908 and 1913 as distinctly different values for these magnitudes were obtained from alpha-particle emissions (by Rutherford et al), from ionization (by Millikan), and from Planck's blackbody radiation equation. This monograph explains how Perrin's measurements of the kinetic energies in Brownian motion were nevertheless exemplars of theory-mediated measurement - the practice of inferring values for inaccessible quantities from values of accessible proxies via theoretical relationships between them. Moreover, though Planck in 1900 had proposed turning to complementary theory-mediated measurements of inter-linked molecular magnitudes as a source of evidence, it was Perrin more than anyone else who championed this approach. The concerted efforts of Rutherford, Millikan, Planck, Perrin and their colleagues during the years in question led to evidence of this form becoming central to microphysics. The analysis here of how this came about replaces an untenable legend with an account that is not only tenable, but far more instructive about what the evidence did and did not show"--
Includes bibliographical references and index.
"Legend has it that Jean Perrin's experiments on Brownian motion between 1905 and 1913 "put a definite end to the long struggle regarding the real existence of molecules." Close examination of these experiments, however, shows how little access they gained to the molecular realm. They did succeed in determining mean kinetic energies of particles in Brownian motion, but the values for molecular magnitudes Perrin inferred from them simply presupposed that those energies match the mean kinetic energies of molecules in the surrounding fluid. This presupposition became increasingly suspect between 1908 and 1913 as distinctly different values for these magnitudes were obtained from alpha-particle emissions (by Rutherford et al), from ionization (by Millikan), and from Planck's blackbody radiation equation. This monograph explains how Perrin's measurements of the kinetic energies in Brownian motion were nevertheless exemplars of theory-mediated measurement - the practice of inferring values for inaccessible quantities from values of accessible proxies via theoretical relationships between them. Moreover, though Planck in 1900 had proposed turning to complementary theory-mediated measurements of inter-linked molecular magnitudes as a source of evidence, it was Perrin more than anyone else who championed this approach. The concerted efforts of Rutherford, Millikan, Planck, Perrin and their colleagues during the years in question led to evidence of this form becoming central to microphysics. The analysis here of how this came about replaces an untenable legend with an account that is not only tenable, but far more instructive about what the evidence did and did not show"--
Brownian movements.
Atomic theory.