Foundations of Modern Atomic Theory: Thomson, Rutherford, and Bohr

According to Schwab (1974) scientific inquiry tends to look for patterns of change and relationships which constitute the heuristic (explanatory) principles of our knowledge. In other words: “A fresh line of scientific research has its origins not in objective facts alone, but in a conception, a deliberate construction of the mind … this conception [heuristic principle] … tells us what facts to look for in the research. It tells us what meaning to assign these facts” (Schwab, 1974, p. 164). Monk and Osborne (1997) pointed out how many science curricula have forgotten Schwab's important epistemological distinction between the methodological (experimental data) and interpretative (heuristic principles) components. Matthews (1994) emphasized the importance of heuristic principles in scientific inquiry and science education in similar terms. To understand the function of “heuristic principles” let us consider J.J. Thomson's experimental work with cathode rays. Although the experimental details are important we cannot ignore the rationale behind Thomson's determination of the charge to mass ratio of cathode rays. This rationale, which helped Thomson to identify cathode rays as ions or universal charged particles (rival hypotheses), precisely constitutes the “heuristic principle.” In a recent study, Blanco and Niaz (1997b) have shown how both students and teachers understand Thomson's experiments as a series of conclusions based on empirical findings (truths). In the case of Bohr's research program, Lakatos (1970) considers Bohr's explanation of the paradoxical stability of the Rutherford atom as the heuristic principle. In contrast, most textbooks consider Bohr's major contribution to be the explanation of the Balmer and Paschen series of the hydrogen line spectrum (i.e., experimental findings). This reminds us that almost 45 years ago we ignored Schwab's (1962) advice that science cannot be taught as an “unmitigated rhetoric of conclusions in which the current and temporary constructions of scientific knowledge are conveyed as empirical, literal, and irrevocable truths” (p. 24, emphasis in original).

The history of the structure of the atom since the late nineteenth and early twentieth centuries shows that the models of J.J. Thomson, E. Rutherford, and N. Bohr evolved in quick succession and had to contend with competing models based on rival research programs. This period of the history of structure of the atom has been the subject of considerable debate and controversy in the history and philosophy of science literature (Achinstein, 1991; Falconer, 1987; Heilbron, 1985; Heilbron & Kuhn, 1969; Hettema, 1995; Holton, 1986, 1993; Jammer, 1966; Kuhn, 1984; Lakatos, 1970; Popper, 1965).