An Appraisal of the Controversial Nature of the Oil Drop Experiment: Is Closure Possible?

Acceptance of the quantization of the elementary electrical charge (e) was preceded by a bitter dispute between Robert Millikan (1868–1953) and Felix Ehrenhaft (1879– 1952), which lasted for many years (1910–25). Both Millikan and Ehrenhaft obtained very similar experimental results and yet Millikan was led to formulate the elementary electrical charge (electron) and Ehrenhaft to fractional charges (subelectron). There have been four major attempts to reconstruct the historical events that led to the controversy: Holton ([1978]); Franklin ([1981]); Barnes et al. ([1996]); Goodstein ([2001]). So we have the controversy not only among the original protagonists but also among those who have interpreted the experiment. The objective of this study is a critical appraisal of the four interpretations and an attempt to provide closure to the controversy. It is plausible to suggest that Ehrenhaft’s methodology approximated the traditional scientific method, which did not allow him to discard anomalous data. Millikan, on the other hand, in his publications espoused the scientific method but in private (handwritten notebooks) was fully aware of the dilemma faced and was forced to select data to uphold his presuppositions. A closure to the controversy is possible if we recognize that Millikan’s data selection procedure depended primarily on his commitment to his presuppositions (existence of e). Franklin’s ([1981]) finding that the selection of the drops did not change the value of e but only its statistical error carries little weight as Millikan did not perform Franklin-style analyses that could have justified the exclusion of drops. It is plausible to suggest that had Millikan performed such analyses, he would have included them in his publication in order to provide support for his data selection procedures. In the absence of his presuppositions, Millikan could not tell which was the ‘expected correct’ value of e and the degree of statistical error. Finally, if we try to understand Millikan’s handling of data with no reference to his presuppositions, then some degree of ‘misconduct’ can be perceived.