Infrared metaphysics: radiation and theory-choice. Part 2

Abstract

We continue our discussion of the competing arguments in favour of the unified theory and the pluralistic theory of radiation advanced by three nineteenth-century pioneers: Herschel, Melloni, and Draper. Our narrative is structured by a consideration of the epistemic criteria relevant to theory-choice; the epistemic focus highlights many little-known aspects of this relatively well-known episode. We argue that the acceptance of light-heat unity (and of the unified theory of radiation more generally) in this period cannot be credibly justified on the basis of common evaluative criteria such as simplicity and standard notions of explanatory power. Whether the consensus was justified by some other criteria remains an open question.

Introduction

In the earlier instalment of this paper we introduced the nineteenth-century debate between the unified and the pluralistic theories of radiation. We made a close examination of the arguments and changing positions of three pioneers in this field: William Herschel, Macedonio Melloni, and John William Draper. All three started with a strong advocacy of the pluralistic theory, which Herschel maintained to the end. Although Melloni and Draper later renounced the pluralistic theory in favour of the unified theory, we concluded that there were no compelling reasons of observational adequacy that should have convinced them to change their minds. In this part of the paper, we make an examination of other possible reasons for the dominance of the unified theory, focusing especially on simplicity (section 2) and explanatory power (section 3).