Classification and the Use of Instruments

Abstract

If the taxonomic changes were the preconditions of the theory choice in the optical revolution, then what were the causes of these taxonomic changes? At first glance, it looks as if these taxonomic changes were caused by some social or political motives: Brewster stuck with the old taxonomic system because he could downgrade the merits of the wave theory, Lloyd introduced a dichotomous system because he could make the wave theory look good, and these tactics were closely tied up with the politics at the British Association. This social or political interpretation, however, has a vital problem. If Brewster’s persistence in using the traditional taxonomic system reflected only his hostile attitude toward the wave theory and if Lloyd’s choice of a dichotomous system was merely a rhetorical trick, then we should expect heated debates between the rivals on the legitimacy of their classifications, but that never happened. The silence of particle theorists suggested that they might have agreed with the main idea embedded in Lloyd’s system. Comparing the three major taxonomic systems during the revolution, we can see that the emphasis on polarization was a common theme, which appeared first in Brewster’s classification, was further elaborated in Herschel’s, and finally reached its climax in Lloyd’s dichotomous system. This common theme reflected the consensus shared by particle and wave theorists during this period that polarization was the most promising research topic. The common practice of the optical community may have been the foundation of these taxonomic changes, but why did not Brewster, who had recognized the importance of polarization much earlier than Lloyd, develop a dichotomous system? This chapter analyzes the cognitive basis for taxonomic choices in the debate concerning the two rival theories of light, and argues that the selections of taxonomic systems by these historical actors were not arbitrary. Brewster stuck to the old Newtonian system not because he was unscientific or irrational, but because his experimental instruments and procedures prevented him from seeing polarization as the most important optical property. Similarly, Lloyd’s dichotomous system was not a rhetorical tactic, but a reflection of the improvement in experimental instruments and procedures.